You're itinerary is looking good for the most part. Don't quite know of any hostels in Waikiki. You might want to try the Pagoda (not in Waikiki -- near Ala Moana) for cheaper prices or use www.biddingfortravel.com for a nice hotel in Waikiki at a reasonable rate.

As far as a vegitarian place to eat, I'm not one, so I'm not aware of any, but there are many restaurants throughout Waikiki that offer vegiterian meals, etc. Try calling the restaurants in advance before going. Have a great MR and with that a great shop stay in HNL.

Oh and boogie boarding rentals can be rented right off the beach or even at many hotels. I know the Sheraton Waikiki Hotel will rent them to you for $5/hr or $12/day. Waikiki can get pretty crowded consistantly from the Ala Wai side to the Kapiolani Park side. If you get out towards Queen's, you might have a little less people (and might be able to catch more waves) but will encounter more locals. In Waikiki, however, I'd say Queen's is your best bet.

Aloha