I couldn't find the answer to this anywhere:
how many points do you typically start with
a) in a casual game
Zero in both cases. You can start with any number if you don't want to deal with negative totals.
While the target score is 25 points, 480 is possible. So triple that for 1440... 2000 points seems like a number safe enough for nearly any game to remain positive for all players.
It's a tradeoff, right? Start with 0 and you typically deal with small numbers; or start with 5000 and never have to deal with negatives.