Well far as hosting I would stay with shared as long as I could!
Until your host says you have overloaded the server which I dont forsee until your site really gets active and then upgrade to a dedicated server.
And for your site purpose, how many members would you need to fullfill the damand?
200'000--500'000---1 million?
That would be the question.
if its only 2 or 3 hundred thousand, You should be fine!
BUT! Its not the fake profiles that will have the interaction. Its your visitors! How many visitors do you expect that keeps hitting the search button and viewing the profiles?
I have a general idea of what you have in your mind about the draw, but most here wouldn't have that kind of knowledge. we all have member bases, not visitor bases.
If you have say only a hundred visitors a day, well than no problem. but if you have one million visitors a day (hell if you have that many, I am jumping on board LOL) then you will have to upgrade to dedicated server I am sure!