How many outlets do I need?

The electrical code calls for sufficient outlets to reach one with a six foot cord from anyplace on any wall in the room without having the cord cross a doorway. That is the minimum standard; you will want more. Figure out how many things need to be plugged in and where you want spare outlets. Take the total and add half again more. In general, the outlets do not have to be on separate circuits except in special cases. The most obvious item is that the load on any one circuit should not exceed 20 amperes. Another is a code requirement that stationary appliances, like refrigerators, be on a separate circuit. Outlets in wet areas need to be special GFI (ground fault interrupt) types. You will probably want a couple of duplex outlets over the sink, which should be of that type. If the solution warmer is away from the sink, its outlet should also be of that type.

In my new darkroom, I have three outlets in the sink area. I have an long outlet strip in the enlarger area that allows me to plug in numerous devices anywhere along that wall. I have convenience outlets on the other walls at the usual places. I also have dedicated circuits for the refrigerator, print dryer, and air conditioner. My safelight will be on the ceiling, so I had the electrician install what amounts to a permanent extension cord for it - there is and outlet box on the ceiling and a line running from it in conduit to another box on the enlarger bench; that box has a line cord running from it that I can plug into the enlarging timer to control the safelight.

When I built my new studio darkroom recently I put in 48 (240V 13amp UK) outlets. My electrical contractor thought I was crazy.
OK, so it doubles as my daylight studio workroom as well, so there is a lot of computer equipment on the dry side, but I find that probably 60% of them are in regular use and the flexibility their placement gives me is very useful.

Also, I have wall and ceiling 5amp plug sockets for safelighting, all with pull switches. I replaced the buttons on the end of the pull cords with wooden curtain pole rings, much easier to find in the dark (make sure they hang just above head height though!). All 13 amp outlets are on a master switch by the door so they can all be disabled at once. All electrical circuits run out of a dedicated GFCI (or as we in the UK call it, an RCD) consumer unit. All main lighting (including daylight bulb fittings for print viewing) is on dimmers.

Only thing I wish I had done is to put the safelighting circuit on a master switch also, so that I could turn them all off without having to go around pulling every cord!

I believe in separate circuits for each enlarger and for "other" like 4 total for 2 enlargers,
so that other elements don't affect them.
i put 4 outlets on each my 2 enlarger circuits, one box each. For the 8x10 that's timer, coldlight heater [ there's something wrong there :>0] and timer. I haven't used the 2x3 in years but the circuit is good for a repromaster's lights and vacuum pump. I put a coupla oulets in the ceiling too for the safelight.