I stayed in a small town local ryokan and it is definitely different. The local farmers had rented a room next to us and drank and sang all night. They invited us over and we had a great time. But, it is definitely a different experience than the western travel experience, so be prepared to go with the flow.

I guess you are not a fan of renting bathing suits. A city run onsen/pool in Beppu is happy to rent you one since you have to have a bathing suit to go into the outdoor(co-ed) warm pool.

You are right, defnitely not my thing.

Standing up whilst performing the pre-bathing ablutions is listed as bad etiquette in all the English translations of what not to do in a sento/onsen that I've ever seen. Reason is that you're more likely to splash another customer. I found out how effective it is just this October when I used the onsen at Takaosanguchi. A Japanese lady was showering standing up (ignoring the shower stalls specifically designed for standing) and the spray bouncing off of her was formidable. Definitely unpleasant.
On the plus side, my young daughter made great friends with a little boy at the baths, I got chatting to his mum (who had lived for a time in Australia) and we spent about 3 hours together. Time flew past, it was idyllic. Seems odd to remember we were naked the whole time.