As a beginner I have decided to have 50 Buy ins for my SnG bankroll leveling ... I think 50-100 BB should be enough to handle few bumps ( bad beats...downswings) on my way ...It really depends on how relax you are as person when having a rough day or two and how can you go to lower limit if it is necessary.
The more the better, and yes 20 is definitely the low end of acceptable.
When I'm playing my normal stake (the stake where I feel as though I can still beat the games but only just) I tend to like to have 50+.How many buy-ins do u go by?