1. hmm, i don't know exactly what you mean here.
but templates and php scripts are tightened together in a good and easy way mostly
2. yes possible, and yes very easy
3. Hmm, theoretically possible, but not with the normal importscript.
you may need a extra script for it, maybe you ahve to hire a coder for that.
4. there is a pda hack AFAIK
5. with .htaccess redirects this should be possible, also with the viewtopic.php to write yourself it should work.
the id numbers aren't touched within the portingscript afaik