Wo, I can see 60+ buyins for MTTs and MT SNGs. I play around a 20+ buyin rule for STTs and a 2% (50 buyin) for MTTs. You really don't need such a huge cushion if you are willing to move down.
*Of course when I move to $10s and above I believe I will switch to a 30 buyin rule.
Many say 20 buy-ins for microstakes because downswings aren't as harsh as higher stakes. However, majority of the people who use 20 buy-in brm still go broke. You do know that 10 buy-in loss downswing is common, right?
Let me provide an example. Assume I have $110. I have 20 buy-ins for $5.5 sngs. Let's say I faced ridiculous downswing of 10 buy-in loss. So now, I'm down to $55. I'm forced to play $2.2 sngs or so according to 20 buy-in brm. Now I gotta win $55 through $2.2 sngs. Even if you're a winning player at the stake who's only facing a little bump on the road, you're forced to move down under 20 buy-in brm.
Now, if I had $550, which is 100 buy-ins and faced 10 buy-in loss downswing. No big deal. Rest up, play again at $5.5 sngs. I can make up $55 through $5.5 sngs, which is lot easier than making $55 through $2.2 sngs.
Making up the downswing loss at the same stake is much easier and better than making up the downswing loss at the lower stake.
This is just my advice. It's upto the OP to see what advice he takes. I personally had trouble with 20 buy-in brm. After reading Leatherass9's book, I decided to take his word for it and try 100 buy-ins. So far, it's been working very well for me.
However, for some people like Tom Dwan, he didn't even need 20 buy-ins. He deposited $50 and jumped right onto $5.5 sngs. I am not Tom Dwan. I don't know what works for the OP but if 20 buy-ins has been working for you, then i'm glad you're doing well. However, I just cannot stand having 20 buy-ins because when I face a ridiculous downswing, I'm forced to move down often and the fact that i have lost half of my roll will psychologically put me on tilt and anger, not to mention how tedious it looks for me to regrind back up from lower stakes. At least if I'm using 100 buy-ins and lost 50 buy-ins, which makes me move down, I won't feel too bad because it's a clear indication that I'm not skilled to beat out the stake I've been playing at. Losing 10 buy-ins can be done because of variance. Losing 50 buy-ins means you're not skilled enough to play at the stake.