Almost everything fails science-based

The most "realistic" alien creations are nothing more than fanciful imaginings. We have one data point: Earth. Everything else is a guess — and not even a particularly educated guess since there's nothing we can use to prove the "education" part of the guess was right. Phrenology was an educated guess.

Having said all that, let's look at your list.

Female gets fertilized by male's "whiptail".

Judgement: unrealistic.

A quick study of birds and reptiles will demonstrate that they mate by rubbing orifices together. It can be quite an acrobatic show (I used to breed birds). But the point here is that you need two orifices: one that ejects sperm and one that collects it and moves it to the egg. (If there are biological outliers to that statement, please point them out in comments! That would be good info for the OP.)

On the other hand, I also once kept iguanas. Lovely creatures. Fun to watch chase the cats around. Not so much fun prying away from the top of the drapes. That whiptail starts off as muscle and bone but it ends as basically skin-covered bone. It serves a few purposes, but breeding ain't one of them. It would be very impractical (unless you didn't describe what you meant by this claim).

Community takes care of female while she is carrying, including feeding her and she will need all that food.

Judgement: realistic.

Assuming that there aren't examples in terrestrial nature of communal caring of breeding females (I haven't take the time to research any — but I'd be a bit surprised not to find one), I can nevertheless easily suspend my disbelief for the idea.

While inside mother, egg absorbs nutrients and other stuff like antimicrobial chemicals.

Judgement: realistic.

This is basically what happens in real life. So you're good to go.

When time comes, female pushes out snot in thick leather (sexy, I know).

Judgement: unrealistic.

What do you mean by "thick leather?" Cockroach eggs are made up of a hard, thick leathery material. This one doesn't really work for me. The female isn't bearing an egg, she's bearing a sack. Can we find an example of a bird that lays a "thick leather" egg? Even if it hardens after laying?

This little snotty is taken care by community, including keeping it watered and warmed.

Judgement: kinda unrealistic

While I can suspend my disbelief for caring for the mother, and I know there are examples in nature of kinda communally caring for infants (sea lions, if I recall correctly), I don't believe there is an example where the mother becomes disconnected from caring for the child — and this statement kinda reads that way. There's a difference between "communal help" and "communal responsibility." I could believe "communal help." I can't believe "communal responsibility."

Snotty inside is practically speaking brainless ectotherm for early phases of deveploment.

Judgement: unrealistic

Brains are needed to control things like hearts, lungs, muscles, etc. Only in the earliest stages of gestation while cell division is still the predominant characteristic of gestation is there no brain. Unless by "brainless" you mean "can't care for themselves" or "can't think," in which case this is totally realistic because that's what happens in real life.

Shorty before hatching from thinning leather shell, their brains began to deveploment little.

Judgement: unrealistic

At least in the way you mean it, it's unrealistic. All creature's brains develop after birth. Most animals are ready to functionally participate after birth — but the brain is still forming. Humans are totally incapable of functioning independently after birth, so ours has the most development to go. However, this statement is built on the previous "brainless" statement and that's just not how nature as we understand it works.

Once little snotty hatches, they practically speaking have pea soup inside their skulls.

Judgement: unrealistic

This is just a restatement of the previous "brainless" condition.

Community takes care of snotty the moron who can't even maintain their body temperature.

Judgement: kinda unrealistic

This is a restatement of the previous "taken care of by community" condition.

As time passes, this kid grows, literally gets some brain and becomes able to main their body temperature like good endotherm should be.

Judgement: realistic

This is how life works. If we ignore your "brainless" condition.

Conclusion

Why is it important for an alien species to be science-based? If it is important, then you're required to use examples from nature to stitch together your frankenstein alien. You can't just invent things and hope they line up with science.

It's actually really cool to use science (in the form of pieces or attributes of actual creatures) to model an alien species. This gives the species the look and feel of a plausible creation without worrying about just how plausible it really is (it isn't...).