I don't know how "I've never heard of a non-Thai foreign national spending the night there" is even an argument. Be humble about what you don't know instead of trying to be a "know it all". No need to shove to people throat your personal preferences, OP asked about staying at that border. He didn't ask you to create a 2 days trip for him.
And fyi, if you have dogs or cats they won't even ask for health certificate or wtv at O'Smach border. It's a very chill and easy border. Yes, 11 guesthouses seems about right. Probably a bit more not on google.
I've been to O'Smach a few time with my wife and our dogs. Nothing weird in spending the night there for a border bounce. I always see other foreigners went I do it. It's not crowded so it's a great option.
Usually mid-way through the 30 days you can, and you need to show up in person. The extra 30 days will start counting after the first 30 days expire. So if your original 30 days expire June 14 and you go tomorrow, you will be stamped until roughly July 13.