I know that my variance in NL is huge compared to limit, since I'm definitely not an expert and my poor plays cause much huger losses. I think for limit the general recommendation is 200-300 BB, as many of the expert players have gone on 200BB+ downswings.
From a quick search of the NL small stakes forum, for those who know what they're doing 5-10 buyins looks to be sufficient for playing on the lowest level. To learn NL, 20-30 buyins is recommended.
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