its ok to do onchain but restrict it to higher value transactions - >100,000 sats to avoid too much dust.

Have a QR code where they can scan. cycle the QR code if you have to spend from the address.

But personally I would avoid it and use lnbits tpos. You can easily train staff how to use it. Liquidity is not your issue unless its inbound.

or you can just use wallet of satoshi and have them manage it all for whatever fees they charge