Hail to my fellow Blood Raven
To answer your questchins:
1). I would say ultrasmurf tactics should do, at 500 pts it dosent matter much.
2). No. Libby is way more fluffy for a blhud rehven force, and a level 2 psyker can wreak havoc upon your enemy in a 500 pt. battle.
3). Depends. If your enemy takes 500 points of boyz then yes.
4). for the leftover 15 points you can take 2 Storm Bolters for the tactical squad seregants and then one additional storm bolter for this razorback of yours
Also i suggest changing the
TL Lascannon on the razorback to either an Assault Cannon, or a Heavy Bolter. If you take the heavy bolter you should be able to take an assault cannon on the dreadnought.