Actually its quit hard, it seems like ever week more and more projets with good ideas start (so its hard to do a good research). So far i have 40 Coins and i plan to keep it at that number, but who knows
Cheers
Diversification is actually a good thing in order to average and mean the profit and loss. However, in my opinion, 40 coins are actually too many. Not sure what you have but 25% of those will be worthless is a while. Better to exchange some of them into more robust ones.
Personally for me, 40 coins is impossible to deal with. I can't even do my things while holding 5 coins. The best is to have different ones, but not that much in numbers. Maximum 10 of them, no more.