1) For a PPL VFR only aid yes, for your (I'm guessing) Commercial programme - no. (APP in aviation normally means APproach Procedural for ATCO's - you've mentioned APP a few times and, in your case, what the h*ll does it stand for?)
2) No - databases are regional. Standard is either Americas or Rest of the World
3) Airliner GPS's have to be BRNAV approved - that means fixed installation. Hand helds that you buy in your local aviation suppliers catalogues don't even come close.
4) No. The only ones you would be able to use are those certificated and approved for the job as well as being installed in the aircraft. See answer (3) above
5) Very
6) If they've got the road database - yes. If it's aviation - no.
7) Anything by Garmin