1. Yeah, most likely gate pressure so your boost controller doesn't do any "bleeding" to 17psi
2. As long as your tune is good and you use the right fuel, you'll be fine. You can regulate boost with your right foot.
3. Maybe AAC valve needs cleaning (or whatever they're called on the RB25).
4. Too hard to diagnose, but maybe someone else can help.
5. That's fine.
6. You'd hope so.
Happy motoring!
*edit* hmm posts before me, meh I'll leave mine.