You have a small space. I agree with the one long 3 foot deep work area. I would go with an Omega or Beseler 4x5 enlarger (I use Beseler).
I think you should draw out everything to scale on graph paper before you start anything. Take into account your vertical space also so that you are sure you have room for the top of your enlarger extended to maximum.
You will need an area to dry negatives so a homemade version of a Jobo Mistral film dryer using a PVC frame and shower curtains would work well. It is collapsible and can be stored away when not in use.
You will need space to dry prints also. You don't have room for drying screens so a retractable vinyl covered clothesline (or two) strung the length of the room will give you plenty of print drying space.
You have limited room to store chemicals. Try to settle on one shot chemistry for all processes so you don't have to store anything beside stock solutions.
You will have limited space for processing trays. Consider single tray processing if you have a good water source and use plastic 2000 ml beakers from US Plastics to hold your solutions while using just one tray.
A floor drain would be ideal. You could build a cart for your print washer and store it under the sink when not in use so it does not hog sink space. You could run tubing from the water source to the washer and then drain it into the floor.
Build a shallow sink that is sufficiently high for your comfort level. Build some vertical slats under the sink for tray drying/storage. Build some horizontal shelves under the sink also for storage of solutions, beakers, etc. If you are handy enough, make the shelves extendable (even though you have only 2 feet for extension) for easier access.
Hang a large dry erase board/greaseboard on the short wall for writing notes. Some are also magnetic and handy for attaching instruction pamphlets etc.
You small darkroom will likely be cluttered and prone to dust. Use semigloss paint that is easier to dust and clean than flat paint. Use a smart floor surface as well (e.g. sheet vinyl).
Under the enlarger, you have a lot of potential space if you use pull-out shelves. You can store paper safes, dodging tools, contact print frames, focusing aids, negatives, etc.
If you are really handy, put a small air compressor in an adjacent room with a switch and outlet hose in the darkroom to dust negatives.
Use a flush, steel, exterior door because it is relatively cheap and easier to lightproof than a wood door.
Pay attention to ventilation. But if you use single tray processing you will have a much easier time with vapors because less surface area is open to air at any one time.
Put anti-fatigue mat material along the length of the darkroom.
Install twice as many electrical outlets as you think you need. Put some under the sink and enlarger (you might want a timer or tempering bath under there). Put some up high near the ceiling.
Ideally you would have some space outside the darkroom for storage, framing, etc.
I would paint the area around the enlarger and its ceiling gloss black. The rest of the room I would paint pure white or pure pale gray.