I've never had a Sukkah heater. What are the YT considerations between the various options?
1, 2, and 3: to make sure it is safe to remain on over YT.
For propane, it means you have a fire on in the succah and can't turn it off. The larger patio heaters will go through a tank in 8-10 hours on high so they won't last through what you need.
For electric you may want to see what fire and overheat protection it has and whether you can turn it on and off with a shabbos clock.