Electrum wallet is not designed to handle commercial use (managing hundreds of addresses per hour) so the number of addresses you want to manage will determine what kind of software you can use.
Performance engineering is what will determine whether it is appropriate to use open source applications or you should start from scratch (if the store is large).
any way you can use BTCPay Server
[1] and inside it you can have unlimited number of stores that be connected to your electrum wallet.
[1]
https://docs.btcpayserver.org/CreateStore/