do not put all eggs in the same basket.
I have read this one somewhere in a different thread and it is really true. If you put it all in one basket you might lose it all with just a blink of an eye.
Does this also apply on wallet? I mean, is it better to split our btc into different wallets instead of using one main wallet which collect all the money we have?
It depends on the wallet. If you are using web based wallet, that can be applied as we all know your coins on a web based wallet was not that safe, therefore you can divide your bitcoins and put it into your desired different wallet. But if you store your btc on a paper wallet, I think it is safe to "put all your eggs on that basket"