My question remains: Once I have several wallets, this number right here (the one that says 100,000 bytes) shows only the holdings of the selected wallet
how do I check the total amount of GB and blackbytes on all wallets?
GB you can check in
http://explorer.byteball.org/, for blackbytes you'll need to check each individual wallet. And, after receiving them, you'll need to create a new backup.
also is there a limit of wallets you can create? (hopefully not..?)
No.
But since you're into privacy for 60 different addresses: how would you ever use the bytes? Sending them to the same address once again links them together.
Why would I send them to the same address? I will request different addresses and make different deposits and different times. This is what everyone in BTC does for example when depositing in an exchange, you want to use an exchange that allows you to have different addresses for deposits.
About seeing the total holdings... I can't check it on the software itself? that's pretty dumb.