You will have no advantage to counting cards if you have got to play to 20/21 or bust
If you are counting cards you need to be allowed to 'stick' many times
I think what is meant by 'infinite stack of decks' is that many decks get shuffled together (as in the proper casino game, usually six), not one deck after another
Therefore which seat you take does not make any difference whatsoever, card counting cannot come into it