Brilliant for space saving and we've seen so many fantastic styles appearing lately - much less traditional and a lot more fun for kids. You can always make each bed the individual childs own taste through bedding choices, popping things on the walls and cushions & throws.

From what you say I think you’ve got a good idea of where you want your plants to be. Most of the shrubs you have listed can grow very big (particularly the buddleia and camellia) so my advice is to check the labels for their name and variety and look up on google for their eventual height and spread and also how to care for them. My feeling is that in a 3m circle that 3 or 5 shrubs (odd numbers always look more natural) would look best depending on their eventual height/ spread then infill the rest with ground cover, bulbs and perennial plants as the shrubs/trees are growing. Do also check what soil and sunlight conditions they like. The acer and camellia are acidic soil loving plants and may need some ericaceous compost adding to the soil and they do best in part shade. You can get a soil ph tester cheaply from garden centers. Mulch the soil well with manure or well rotted compost to give new plants a really good start. I Also think you’re doing the best by starting with young shrubs as they will adapt to your soil and conditions much better than larger specimens. Good luck with your gardening, I myself have dug a great big hole in the lawn as I need to get my seedlings somewhere:-).

I think Rachelmidlands is spot on if the other ikea colour is ok. If not, it is worth a try but definitely not with chalk paint. A few years back we built a window seat using some Hemnes tv benches and I wanted it to match my hand painted wardrobes (!) Anyway I lightly sanded (black and decker) the finish just to give new paint something to grip. I then did a coat of a really good primer - I used mythic but I know Zinnser is good too. Perhaps go to a specialist decorator centre and ask for the best they have. I then did 2 coats of a Dulux trade paint to match wardrobes. Worked perfectly and lasted until we sold the house- and the seat was considered a feature!

I think this might be the quickest/cheapest option. Assuming the space is big enough and is constructed in the same manner as the rest of the house (not single skin like a garage etc). Remove the door and replace with a window then build a wall to separate from the kitchen. Couple of days work plus decorating time.