20 buy-ins for cash games and 40 buy-ins for tournaments is still
a little bit of a gamble, not bankroll management. Online I would say you need at least 100 buy-ins for cash games. You probably need more than what I said, depending on the stakes you are playing and your level of game play. Of course if you are crushing the limits you can play with 50 buy-ins also, but you have to be absolutely sure you crush the limits.

When it comes to MTT's you need a lot of buy-ins to be safe. MTT's are huge variance and even if you are a top player, you can still end up loosing sometimes around 300-500 buy-ins, so be careful. That's why most MTT players use backers (investors in players which they split the profit with) to be in the safe zone.

As for SNG's, depending on the limits, it's the same thing almost as in the cash games, it depends on the limits that you are playing. SNG's are more softer than cash games tough most of the times.

Can you play with crypto on america card room? Is it open for our country? :)