DO NOT USE DRUNK TANK PINK FOR A ROOM! Sorry, Groveraxle, but further down in the site you linked to it said, "Prisoners did respond and calmed down, as hoped, initially. Major goof: If they hung around too long, they became even more violent." Some police depts. have a pink room, but are cautioned not to let anyone remain in it more than 1 hour. It's called the rebound effect. I read about this while working for a state police agency.

Three bedrooms will always be worth more than 2. If there is enough headroom I would take loft stairs up above the main staircase - from the cupboard position. Leave a landing and corridor to the bathroom and partition off a tiny bedroom/nursery/study. A lot depends on which way your roof is pitched. I would get a few loft companies in to tell you what is possible within a limited budget. If and when you get the money it might be possible to close the existing back door and refigure the kitchen units to allow a lobby and door opening out toilet and use the toilet door as your back door. A downstairs toilet is heaven sent when you have children!

The options are endless. I would suggest doing a search on Houzz for the rooms and style you are thinking of and getting inspiration that way.

Check with the supplier of your new doors. These have to be a certain thickness and fire rated with a loft conversion.