Conservative style: Stay between 30 and 60 buyins of whatever you do.
More unorthodox: min 20 buyins.

Think about it this way: if you lose 7 straight games while at 55 buyins, you'll still have 47/55 of your roll left. And you will lose 7 straight at one point.
If you lose 7 straight while your roll is 20 buyins, you'll have 13/20 left.
47/55 > 13/20 = you'll play more comfortably having more of a roll backing you. This is seriously the only way to play if you want to make $10,000.

Okay, so your goal is just that: get to $10,000. Hey, my goal is to buy a house in Monaco for 8,000,000 euro's, but anyway.
If you put $50 of your "can lose money" to try and get there, and lose it, your roll will actually be -$50. Are you with me still?
Now, you could afford to lose some money like that, trying to learn the game. That's fine. So you deposit another $50 of your "can lose money". You manage to triple it up then move up in stakes. You get bombed there, and lose it again. So now, your bankroll instead of being $200, is actually -$100.

Rinse and repeat and you'll see where I'm going.

Nothing is as important in poker as BR MGMT. Okay, maybe laying second best hands down, but nothing else is as important in poker as BR MGMT. Nothing.