1. No. Your other purchased powers will start at level 1 (50% power) and will be leveled until they hit their cap (whatever that level is) where they will be at 200% power.
2. Yes, but you won't be able to further modify/enhance it (its already basically more powerful than constructed power can be).
3. Yes, power copies of mages will copy their gift/affinity/etc. With manager/Prototype you might be able to alter/merge/etc. the various copied magic powers into something more comprehensive or whatnot.