What about the custodial issue? We can not expect that a beginner in Bitcoin will be able to set up a LN node the first day.
Phoenix and Breez are mostly non-custodial. By "mostly" I mean that the parent company may only be able to steal your money during opening a new channel. However, I find that the risk that the company turns evil in exactly those 10 minutes when you receive your $5 payment is negligible. Also you need to open the wallet at least once per week to check for fraudulent channel closing. But again, the risk is negligible.
I know that the more efficient way to send SATS is on the lightning, but for a beginner do you think that is it easy to get their first SATS on the LN?
There's a channel opening fee (2 ksat in Breez, 3 ksat in Phoenix). If you orange pill a store, just add it to your bill.
IMO show them Breez. I dislike unencrypted backup to Google but it allows Breez to not ask the user to write down any words. Check out its Point of Sale mode, it's exactly for the merchants.
Is the business willing to hodl the SATS received as payment or want to exchanged for FIAT asap?
Depends on the business. But you should accept them either way. Rikki6ixx wrote a rant about doing otherwise: https://bitcoinitaliapodcast.it/missione-centro-america-2022/day-27-egoism