And would it matter if the 5 BTC in the moment of fork was on my private adress/wallet, OR if it was on some agregated BTC adress/wallet (like on an exchange like bitstamp for example)...? Even in this case i would still own 5 BTC on BOTH chains?
Of course it matters.
If you aren't the sole controller of your private keys, you don't have any bitcoins.
If your coins are held by an exchange, you have IOUs, not bitcoins. In that case, if a contentious hard fork occurs and two chains survive the split, the exchange decides which coins you receive. They may let you withdraw your coins on both chains, or they may choose one for you and keep the coins on the other chain for themselves. This is just one of many reasons why no one should ever use an exchange as a wallet. If you want to trade, fine, but when you are finished, withdraw your coins to an address that is exclusively under your control (or risk the various shenanigans which tend to occur at exchanges / central wallets).