Alaskan Excursions, Newbie Questions...

Greetings:

I've booked my cruise, (Pricess Voyage of the Galciers) and now I'm
looking at the various excursions.

From lurking here on the group I've already picked a Whale watching
excursion in Juneau but I have some questions on the other ports...

1. Assuming the timeing works out, is there any reason I could not
book an excursion with a diffrent cruise line (ie RCL) if they had
something I liked better than the Princess offerings?

2. As a general rule is is possible to book two or three shorter
excursions per stop or do the pre-set start times preclude this?

3. Should I spend extra time reseaching private excursions or are the
cruise line offerings a "good deal".

4. If I have a bit more to spend, Are there any "vip" excursions
avalible via the cruise line or stand alone? (ie. smaller groups,
faster service, etc... )


Thanks.