Position based on this challenge is important only the first hand played when you should bet second (last), position betting last on the final hand is not applicable with circumstances the poster stated, the last hand is unknown.
This challenge includes an infinate number of hands so no prior knowledge is known when the final hand will occur, thus the final hand position upon seating is irrelevant.
Playing (betting) second the first hand is advantageous if your opponant makes a large or all in bet, you would want to make a lesser bet to take the low as a fresh shuffled deck(s) is negative expectation for both players.
it doesnt matter if he goes all in because even if he goes up to $1250 (all in with the $500 and getting a blackjack he still will need $3750 more to win, I cant see a situation when going all in would be advantagous unless you are down to a few bets and he has a lot of bets left. also i think position may switch throughout the challenge because i doubt it can be all played out in a day