Hello there, uamtgr.
If you're referring to bank accounts, you can connect multiple accounts in QuickBooks Self-Employed. When linking your bank account to QuickBooks, you can read this article for the detailed steps: Connect an Online Bank or Credit card Account.
On the other hand, if you mean on how many QBSE accounts you can sign up, it's okay to have one. Though, you can still sign up another one using the same credentials.
Also, you can check these article for additional reference in handling transactions in your account:
If you're referring to something else, please let me know anytime. I'm always here to assist you further. Take care!