Ante size of $0.50 is good for $3/$6 or for $2/$4. A $0.25 ante wouldn't be bad either, but I'd prefer the $0.50 myself. As a rule of thumb, you want your antes to add up to one small bet, give or take. Less than that, and it encourages nitty play. (n) :thumbsdown: More, and it encourages looser and more aggressive play. (y) :thumbsup: Up to you.
Highly recommend going the extra step and making it a dealer ante of the amount of the small bet to keep it simple. It'll be a little too big if you go short-handed, but you can always adjust if that happens.
As
@Shaggy said, $200 is fine for $3/$6 (I'd say $100 is a little short).
@BGinGA is just trying to make people put tons of chips on the table. Buying in for 50 big bets in way more than you need to play right. Such fun chip mountains, though.
You could do $2 and $5 betting limits if you want, but it'd be unusual. More common with low-stakes Stud is spread limit, say $1–5, $2–6, or $3–10, where you can bet/raise any amount within the specified ranges in any betting round. You could also do a structure like $2/$4/$6 or $2/$4/$8, where the third limit is an extra-large bet on seventh street only.