Excessive buffer is bad and can lead to a lot of ridiculous "phantom" inputs to cover up what should have been mistakes, or inputting attacks ahead of time and hoping you guessed right. Buffering makes it easier to play the game "perfect", because you won't need frame perfect timing to successfully make inputs that have a 1-2 frame window. Keeping it small is good: honestly I'd probably stick with anything ranging from 0-2 frames of consistent buffer.
L cancelling... eh. I personally don't think there's a need for it. The game would be the same whether you had an input for L cancelling, or whether the lag reduction was naturally applied. The only difference is that a few people that fell short on the technical end would be evened out. Which doesn't mean they will strategically or fundamentally be as good as the other guy. Like, automatic L cancelling won't somehow flop the tables and mean my little brother will now suddenly beat me. If the one advantage I DID have was L cancelling, or that the only reason I was winning was due to superior execution at it, that's kind of a dumb reason to be winning lol. And I don't think that's the case. There's a difference between no L cancelling, and L cancelling as far as punishes and combos and overall gameplay goes, that's true. But the difference between automatic L cancels and trigger L cancels isn't drastic or would flip the game on its head. In fact, having it automatically done might let people focus more on the fundamentals of spacing or looking deeper at where combos will take you since the technical aspect isn't as forebearing.