StephenG has already covered most of the reasons why your sapient species might be plausible, so I'll instead focus on how it might evolve.
I expect that your aliens will likely resemble owls more than anything else. Owls, after all, are predators with good night vision (like cats), excellent hearing (like rabbits), and the ability to hoot. So, to start off with, you need owl-like bunny-cats. I'd need to know a lot more about the ecology of your planet to determine whether that makes sense, but I don't think it really needs any explanation. Bats are halfway there already.
The real hurdle is this: how does a species evolve sapience?
The current best-guess theory for how humans evolved sapience goes something like this:
- Primate has reasonably strong and dextrous hands (because its species climbs trees all day).
- Primate smashes a couple of stones together, creating sharp edges (whether by accident or for some other purpose entirely- some modern apes have been known to break open rocks to lick off the dust produced... for some reason).
- Primate discovers that those sharp-edged rocks are useful for hunting and/or butchering meat.
- Primate learns to use fire to cook meat, making it easier to digest.
- Primates with larger brains due to random mutations can be more successful, since they have a larger energy budget due to #3 and #4.
- Those larger-brained primates can make better stone tools, allowing them to hunt and cook even more efficiently.
- Their descendants can support even larger brains.
- So on and so forth.
The essential quality of those initial primates, according to that narrative, is their strong, reasonably dextrous hands, which allowed them to create crude stone tools and get the whole cycle started. That's where your bunny-cats might have an issue- neither cats nor rabbits have paws evolved for grasping. However, if they are owl-like nocturnal predators, their legs and feet might resemble those of owls and other raptors, with long, sharp talons optimized for ripping apart prey and for perching on tree branches.
My theory is this:
The owl-like bunny-cats evolved in a jungle with an extremely dense and thick canopy. By day, they hunt rodents on the ground, monkeys in the trees, and so forth in the understory, where it remains dark much of the day due to the thick canopy. By night, they take to the skies above the canopy and prey on migratory birds, perhaps somewhat like falcons do, although they'd focus more on silence and camouflage (with jet-black fur) to catch unsuspecting prey unaware, rather than sheer dive speed. However, the canopy is much too dense with branches and vines to fly through, so they must fold up their wings and climb. Their feet have sharp raptor-like talons optimized for shredding prey and plucking birds out of the sky, while their ape-like hands are better suited for gripping tree branches. They don't have retractable claws, so gripping branches turned out to be more efficient than cat-like clinging with their foreclaws (which are still quite substantial). Their hands also allow them to pick fruit, which they sometimes need to do when they can't find prey.
Climate change forced a population of these bunny-cats into a dry, open grassland. While they still spent much of their time going after small game, the most successful were those that hunted in flocks to bring down large game, such as the local varieties of rhinoceros and antelope. At some point, they mastered the use of fire, allowing them to evolve larger brains and better coordinate their attacks. They later began using stone tools, first to scrape the meat off the bones of their kills (because roasting meat bone-in causes problems, for some reason- maybe heating the bone releases toxic chemicals?), and later to use as spear points. With spears, they could take down even the local lion-equivalent with little risk of being mauled. Fire and stone tools let them power even larger brains; larger, more powerful brains let them make better tools.
And the rest, as they say, is history.
Now, for each of your bullet points one by one:
Cat-like eyes, binocular vision,
Sure. They evolved from nocturnal hunters. They'd have to have pretty good binocular night vision; while cat-like eyes are not the only way, they are one way to do it.
a lot of variation in eye color.
Easy. At any point in their evolution, would some of them find individuals with unusual eye colors attractive? If the answer is yes, there you go. Do note that they likely won't begin to show different colors until they're well established as social fire-wielding hunter-gatherers. Before then, each individual needs camouflage. Afterward, only the hunters will need to be camouflaged; and eventually, even they may not need to be.
Bunny ears, extremely good hearing, length of their ears varies.
Once again, if they're nocturnal hunters, they'll have to rely as much on sound as on sight. They may need to be able to fold their ears down when flying, though, to reduce air resistance. Or maybe not- some owls have prominent earlike tufts that don't seem to give them any trouble.
Cat-like noses, although some individuals have noses that resemble a
cross between bunny/cat nose.
Sure. If their jungle-dwelling ancestors have cat-like noses, there's no particular reason for that to change.
Their languages consists of long short
vowels, which are very similar to hooting noises. They are technically
able to mimic human speech.
Well, I did make them owl-like :)
Many Earth languages have a rich variety of consonants, simply because the human palate and voicebox are able to create a wide variety of them. However, your species could have a purely tonal language, encoding meaning in the pitch and duration of hoots, as well as the duration of the spaces between them. It might sound like Chinese... or like birdsong.
They have short/sleek fur on their face,
arms, and chest. The rest of their body has full fur.
Owls appear to have pretty fuzzy feathers so they can fly silently; your creatures could use fuzzy fur for the same purpose. I have no way to know if the arrangement you've described would work better than any other arrangement... but fur has weight and doesn't contribute to lift, so there's evolutionary pressure for it to be as short and sparse as possible, while also being as silent, aerodynamic, and insulating as needed.
Their skin and
fur are very sensitive to changes in air currents.
I'm not sure how useful this would be. Their eyes and ears will detect predators long before their fur will, and in flight, any useful stimulation coming from the skin will be swamped by the wind. Their wings will provide all the feedback needed for flight. However, cat-like whiskers could be useful for navigating tree branches at night, if they don't cause too much drag.
The palms/soles of
their hands/feet are leathery and have tough oval claws.
Sure. That has precedent in Earth's animal kingdom; it's certainly possible. Though I'm not sure what you mean by "oval claws".
Omnivorous.
Sure. If they evolved the way I outlined above, they'll be mostly carnivores- but if they can eat fruit, that could help them get through periods of scarce prey.
Good sense of smell for finding food.
Cats certainly do, so no problem there.
Warm blooded. Their babies are
born, not "hatched".
Earth's animal kingdom has an entire class of warm-blooded live birthers, so no problem there. Even bats fall in that category, so flight is clearly no barrier to either qualification.
Average height around 2-3.5ft, wingspan varies
between individuals, but is usually between 6-7 feet long.
You've got 47% of Earth's gravity and 62% of Earth's atmospheric pressure. Therefore, flight there will be about 0.62 / 0.47 = 32% easier there as it is on Earth.
Great horned owls have a 4-foot wingspan, on average, and weigh around 3.1 lbs. Scaling that up by a factor of 1.625 gives a 6.5-foot wingspan, with the ability to support about 8.2 lbs in Earth gravity/pressure. Mass goes up with the cube of length, but wing loading is proportional to the wing's surface area, which goes up with the square. So in order to match the flight ability of great horned owls, your creatures will need to have proportionally smaller bodies and/or larger wings.
The gravity and pressure on your planet will compensate for that somewhat, but not completely. They could weight up to 10.8 lbs and still fly as well as owls do here. Great horned owls, I should point out, have proportionally the highest wing loading of any raptor (source: the second paragraph here), so too much more weight and they won't be able to fly at all.
Getting a height of 2-3.5 feet while also having a 6-7 foot wingspan and weighing no more than ten pounds will be... difficult. Especially since bat wings are heavier than bird wings.
Their wings are leathery.
Bats' wings are leathery, so no problem there.
Females tend to have slightly longer wings to support
their weight while pregnant.
Once again, plenty of species (including great horned owls, incidentally) have females larger than the males. I don't know how often baby weight is a contributing factor, but I suppose it could be.
