Nice and Neat Theme , phpBB is known for its simplicity
1) You need to get some good members...try giving them some kind of goodies for posting their ads , not physical gifts instead you can offer a 1 week sticky Ad post for the member who has the highest Refferal etc..
2) Offer some banner Advertisements to make some revenue out of the forum
1) Yes work a big time on the Header and your logo you have a Great Domain make full use of it..
2) Try some Sidebar plugins which can show some latest Posts