Question:
Don't want to test this or search for it so just asking it:
I've updated wallet.dat after I made x(amount) of regular addresses, stealth,... but what with the tokens??
The tokens don't need an extra update of the wallet because they're linked with the stealth address or am I wrong ??
Yes, I believe this is how it works. dasource confirmed this in an earlier post of his.
Just for sake of clarity

OK, so every time I convert Shadow to SDC I create a new SDC address.
Yes every-time you send coins (shadow or SDC) to a stealth address it will generate a new SDC Address
Is this a new private key?
Every SDC Address has a new private key, however because this SDC Address was generated by sending coins to a "stealth address" aslong as you have a backup of your wallet when you created the stealth address you do not need to back it up again. All future SDC addresses created by sending money to that "stealth address" are covered. This is a bit like a HD wallet but not quite ...
Obviously you can never be too careful so backup as necessary.
It seems like over time I will have hundreds of keys and stealth/public addresses in the wallet.
Yes but as per above, if the funds where sent to a "stealth address" then it does not matter as you can re-create those SDC Addresses and corresponding private keys from your stealth address backup.