Yep, RNG is a huge factor and your biggest way to mitigate it is to bet low. Only time you can't do that is against enemies with Ante-Venom (wow that pun hurts even after all these years).
Up to you, I think I usually aimed for a certain percent of the chips I had. That way if I did poorly I'd decrease my bet and if I did well I'd increase my bet. The larger percentage of your bankroll you use, the higher likelihood that you run out before ever seeing the positive returns. This is tied to the concept of 'risk of ruin' in gambling/stock trading.