Hi, I can help a little with your regulator questions.
Some people use acetylene regulators because the scale is relevant for the sorts of pressures you would use with these torches. Propane regulators I've seen go to much higher pressures than the 5-10 psig you would use.
I think the difference in price you might be seeing for some regulators is the difference between a single stage and a two stage regulator. Someone else will need to reply about which to use, as I have an oxycon instead. A studio I often work in has two stage regulators, but they run all the time and for more applications. It might depend if this is a hobby or a job, too.
Good luck and welcome to the addiction
I do agree with Helene, and if you can afford it, I would go for newer regulators. Seals fail, diaphragms fail, and I guess I would wonder about the history of these tools.