For this you can look at underground bunker floor plans to get an idea of what space limited people need. A floor plan similar to this 10x30ft (600 sqft) bunker could easily accommodate a 2-3 person crew's living space needs.
Life Support Needs:
In general, any mission as short as 5 years is better off using stored food than trying to grow it. Growing food takes a LOT of power per person, uses up a lot of space, and needs a lot of specialized equipment that might malfunction before your mission is over. The average person needs about 2 kg of food per day, and food weighs an average of about 1g/cm^3; so, for a 2 person, 5 year mission you need 7300kg of stored food which has a volume of about 260 cubic feet. The average person consumes about an equal volume of other consumables to food (toilet paper, soap, cloths, etc) So you could actually cram your entire consumable needs into a storage space about 8x11x6ft; though, for organization reasons, assume you need walkspace to get to everything. So what you really need is a storage room that is about 200-300 sqft with a ceiling about 6-7ft high. For comparison to farming, you would need about 2000sqft per person to grow your own food during the mission even using stacked aeroponics; so, for a mission this short, just bring the non perishables.
Air and water recyclers are not that big for a two person crew. They'd fit into the flooring or walls of your habitat rather than needing a whole module. You'd probably need a few hundred gallons of water to cycle through and some extra air storage to compensate for any loss of atmosphere over time; so, assume maybe an extra 300-600cuft of space for some large tanks.
Since you are not growing food or running extensive scientific experiments (like ISS), your solar needs would not be anything extraordinary. However, you will need to know how far you are from Alpha Centauri you are. Assuming you are aiming for dead center of the goldilocks zone, you can assume similar energy density to getting solar in orbit of Earth. That said, Earth's atmosphere absorbs about 50% of light before it hits the ground and we can not maintain peak daylight for more than 5hrs per day; so, satellites can get a lot more power out of solar than we can on the ground. Infact, a 600cm^2 solar panel in space can produce enough power for a standard American Household. Obviously, in space you need a lot more power to run your recyclers and climate controls, but in total, you'd only need a few square meters worth of solar panels to run everything.
Lander & Lift Fuel:
The specs on this will have a LOT to do with the planet in question. Earth like worlds need HUGE rockets to get off of. The average Earth rocket needs 83-96% of its mass to be fuel; so, even small space stations need huge rockets. But a smaller world like the moon could use something like the Apollo Lander which is more craft than fuel. See The Tyranny of the Rocket Equation to get a better grasp on how to figure this out for your situation.
All-in-all, I'd assume your station only needs a pressurized volume of about 6000ft^3. This is ~5 times smaller than the international space station; so, you could for simplicity just ignore everything I said and scale ISS down 5 fold.
Your lander may need some hand wavy fuel source if you are orbiting an Earth sized planet, Otherwise it will need to be bigger than your whole station to get to the ground and back.
Humans also don't do well in Zero-G for as long as 5 years; so, you'll need some manner of artificial gravity. Centripetal force is often used in Hard Sci-fi to simulate gravity, but this station is much too small for that to be practical without doing some very interesting engineering. In general, any spinning vessel that is too small will have significantly more simulated gravity at your feet than head which would is quite disorenting just in the short term. In the long term who knows what kind of health issues it could cause; so, again you may want to consider hand waving in some "gravity plating" or else your station will need to be very heavily engineered around solving the gravity issue.