Well, I ended up buying two more wii u pro controllers for a total of three. They really work great. They connect each time with no problem. I have not had to pair them multiple times. They require no changes to the default recalbox.config.
We have played several three-controller games such as guantlet, mario kart and super smash brothers and had no problems.
So the recommendation of this recalbox noob is the wii u pro controller. Be sure to get an OEM one - not a knock-off. They are a bit pricey, but the last two I got were refurbs from ebay and they look and work great.