Every man his own currency you may think in these modern times...and even more confused when sites like XAPO offers collective Wallets and sites like BitMixer offers a Wallet of mixed currencys.
Can someone please explain how to act with theese to be on the safe side?
You are getting these points wrong.
Xapo is a Switzerland-based company that provides a bitcoin wallet combined with a cold storage vault and a bitcoin-based debit card. (from Wikipedia) and Bitmixer is a mixing service wherein you mix your coins in different wallets so as to conceal any traces of you and where the bitcoins will be after the mixing process. To simply explain this, Xapo is a wallet provider and Bitmixer is a service to help you cover the traces of your spending.
A mixer is also good if you are super rich, and don't want your money associated with your address (to avoid being a hack target for instance).
Unfortunately I do not have this problem.
I think that online wallets are pretty safe, but if you have anything more than 2-3 btc I would seriously look in to getting a HW wallet. I like the ledger, and they even have a pretty cheap version for ~15$. But to me it depends on how much funds you have because at some point you don't have enough to bother with all of the super high tech security measures.