My "darkroom" is in the family workshop used for everything from school projects to wood working projects. I set up the enlarger on the workbench with the developing trays beside it. I also have two dishpans partially filled with water on an opposite shelf for prints to soak till I have enough to take them to the bathroom for running water; often I have to wait for somebody to get out of the shower anyway. For safelights I have two plug in night light holders with red Christmas lights. I also have an LED truck bumper light but it isn't really necessary. Works OK, although paper will begin to show fog with the LED light after about 5 minutes. Haven't noticed any fog from the Christmas lights. I used 11x14 size trays to minimize splashing. Prints come out of the fixer and go into the first dishpan for a couple of minutes and then into the second pan till I can get in the bathroom.
It works very well so far. I can set up and tear down in 5 to 10 minutes. All the trays and other gear get rinsed in the shower when I am done. The basic idea came from "The Photographers Handbook" by John Hedgecoe (1979 - the book that started it all for me) On page 62 he gives ideas for an under-the-stairs closet darkroom.
On advantage I may have that you might not enjoy in Tokyo is that I have not had to do anything with the casement windows. Living in a rural setting, i simply wait until it is dark to do any printing. OTOH, I have had kids walk in the door at just the wrong time while I am working and have not yet seen any ill effects. (They don't like the lecture that goes with it :-) But it has also gotten some of them interested in the process - my 19 year old now develops many of my prints and my 17 year old has temporarily ditched her Nikon P&S digicam for the Canon AE-1P. (First roll was bad - what do you mean I have to FOCUS?) LOL.
A caveat on the LED safelight. You can get the 6 LED model that I got at Wally World for $8 or $9, but it is very bright. They had a two or three LED model for less $$ that might work better. You will need a 12V adaptor or battery for that if you want to go that route. The lights are easily small enough to have a friend ship to Tokyo if you cannot find something there. Fifteen years ago when i was last in Tokyo they didn't have Walmart but maybe they do now.
Have also only processed RC paper. I have no idea how well fiber paper would work but am am thinking of trying some in the next few weeks.