I have no recommendation to meet your use case, but I do have experience supporting environments that process credit card transactions. PCI (Payment Card Industry) compliance is going to be a requirement you’ll want to keep front of mind if you’re going to be assisting. PCI doesn’t care too much about the software in use, so long as the network and data handling is up to snuff. For small businesses, this usually means you’ll be limited to a few choices based on the card processor you select.

Pro se means they’re representing themselves. Probably because of no money.

The linked page uses the Mifflin-St Jeor Formula which appears to have been published in 1990. As someone acquainted with eugenics but not how BMR calculations play a role, could you share some I formation on how the two are related?