Loft capacity

It can be done but its allot of work, and it depends on how much room above the doors you have aswell but if your having the loft converted with a new roof then maybe think about lifting the roof up that bit extra

Not without a lot of work.Pretty pointless exercise in my opinion.

Yes you can- we have done this in situations in the past where space is particularly tight in the loft. You could also consider just lowering part of the room- for instance if you are converting in a typical Victorian terrace there is often not much point lowering the ceiling in the front half which is generally all under the eaves.