: Will the kitchen be too cramped?

In a word, YES!

Hi Niklas

I built an 18 1/2' kayak in my living/dining room area and it's about 28' long and 9' wide at the narrowest point. I had plenty of room, but like others, you HAVE to get to both sides of the boat to work effectively. And unless you have a one-sided kitchen, you will need to get to both sides of it as well. There just isn't enough room to work well and also to eat. The health issue is also VERY valid. I was always cleaning dust off the counters, stove and cabinets. It's a mess!!!

(i.e. should I try to renegotiate on the
: living room???)

If you can, I would suggest you try. ??
Maybe just a corner of it, and you could do a "take-apart" as was suggested. A couple of folks here have done that quite successfully. You will add some extra weight with the extra bulkheads, but we're talking a couple of lbs. or so.
If you CAN build in the livingroom/diningroom areas, hang plastic from the walls and over-lap a couple of pieces to block off doorways to the rest of the house, especially the kitchen. Keep the dust confined to the immediate work area.

Do you have a parking area at your apartment and would you trust the area enough to build outside, under cover of a frame and tarp type setup?

I am not an advocate of breaking promises, so I wouldn't go behind her back to do anything. If she is not totally against your building indoors, then you may be able to work something out. ?? ( promise to have it all back to PERFECT condition upon her return. And keep that promise.
If you are alone there, you don't need all the furniture and can relocate some while working. Replace when done. ( take pictures so you will remember where it's supposed to be )

Best of luck!!

Rehd