1.) if you can run btcpayserver, please do! It's much better. 2.) if you only have a cheap php hosting, you might want to run something simpler 3.) you can provide the service for others, it just can't be a business. So both btcpayserver and @Cashu Pay Server can be shared, if you don't make fees and it does not qualify as a business according to local laws. Of course check local laws, but in a few countries that I checked (with lawyers), you can still provide it for others, it just can't be a business 4.) you don't pay with nuts with @Cashu Pay Server ! It's a lightning gateway. You can try it on the donate part of the page, you'll go through the checkout flow!

Yes. You can either run a mint, or enable auto withdrawal to your own wallet though, which happens right after the invoice is marked paid.