Im not sure if it affects you, but ive found i can have a building, build roads close to it around it, then if i demo it i cant fit it back in again if i try to rebuild.
Its couse of the damand for low wealth I build arcology mostly for my great work. Lets me make nice highwealth populations and still keep my industry or specialisations going.
I can answer the second part at least, yes the future buildings will futurise the city nearby them but the futurisation is only cosmetic, however the change in the road from future to normal can be a bit jarring couse they are very different but again its just looks. Ive basically only built classic citys till now even with the expansion available, just now building a futurized city, diving right in with a massive mega tower city