Definitely not a shared nor a reseller package would work for you. I never recommend anyone who has over 500 members to use a reseller/shared package. Especially when you over over 300 people on each day. Go for a dedicated server. Generally something low end, say a P4 with minimum 512MB RAM should do it for now.
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If you stay on those limits a shared host would be enough, however, take in mind that you're near to the boundary where you should start looking on a plan to the future, depending of your growing rate, when you reach the 50 mysql connections at the same time, it would be time to move to a dedicated server
I was with dreamhost on their starter package for about a month, it was pretty good coz i never knew when my forum would grow. As the member base reached over 4000 and avarage visitors tagged about 300 i got all sorts of trouble. I am now on a VPS with slhost