Up to 25 pounds is okay.
Heartgard is a good drug. What some people don't realize is that Interceptor/Sentinel with the 2-10 pound dosing is actually also an 'overdose'. 1/5 of the dose would he adequate for heartworms. The other 4/5 is added for intestinal parasites. Point is that both drugs are technically given in excess.
Sentinel year-round here and Frontline or Advantage if needed. We don't have a tick problem.
If a vet brought two colleagues in to try and talk me in to giving a vaccine (except rabies) I would leave.