There's no set guidelines and it depends on a number of factors eg. how spammy and commercial your vids are, do you have links to CPA offers in the descriptions, do you spam keywords in the desc and tags, do your vids get flagged / disliked etc etc. I only use 10-12 vids per account and have LOTS of accounts. That's quite low compared to some people but I also hardly ever have accounts banned and I have a pretty stable Youtube income.
The other advantage of using lots of accounts with few videos is that you take less of a hit when a given account gets banned.
Just experiment. Try varying methods with different accounts and work out what the threshold is for uploading for your particular style and method. It's like everything else - you have to experiment and fail a few times before you hit the winning formula.