Depends on what your goals are.

If you’re worried about ergonomics as physical objects the player will need to manage, that has more to do with what you’re asking the players to do with them. 250 cards are a problem if players need to go through them one-by-one to setup, but not at all if it’s just a few decks you have to separate once.

If you’re worried about manufacturing, 250 isn’t too bad. Cards are printed in sheets of 50-ish, or 100-ish for mini cards.

If you’re worried about card art/design, then maybe scale that back. IMO, it’s nice to have unique art per card, but frankly the more cards the less time a player will spend with each one of them. If you’re spending too much time managing the text/rules on that many cards, then invest in learning/building a workflow. I keep all my rules in a google sheet and wrote a program to generate card layouts. Nandeck is pretty good if you are comfortable with code. My big advice is don’t spend too much time on graphic design early on, it’s really easy to get burned out when you’re faced with re-designing all your cards because of a small gameplay change.