Along with time, white color turns to be somewhat yellowish. Area needs to be repainted timely. To avoid yellowish tinge for long time use oil based colors instead of water based.
Two most popular options for garage floor coating are epoxy paints and latex paints but the most recommended is epoxy paint. These paints are water resistant and stick firmly to concrete.
I read somewhere that for new and powdery surface use 1 coat of Oil Based Sealer and for normal and sound surface apply 1 coat of Water Based Sealer. After using sealers accordingly, apply 2 coats of Algae Resistant Emulsion.
Remove old plaster and then prepare wall accordingly otherwise paper will not stick properly and will wreck out after a short period of time. I am with roughcaster.
According to me, you should use brush for roof painting. It will take time but will give better result. Roller should be used for second paint coat as small pore impressions are formed by rollers and sometime paint is not applied properly. Plaster will be reflected if roller is used at initial...
I have used other paint gloss too and faced the same problem. I think as time passes paint gives a sign of yellowish tinge. So it should be better to repaint it after certain interval of time.
It will remain cold for some time but what will you do in hot season? I think Douglas is right use bigger rad. If you are not satisfied with it then go for your choice.
Only single ventilation is not good enough. I think proper air and sunlight should enter a house so that everything remains dehydrated otherwise some dampness will remain. It also tears down the walls.