The general rule is to get a trailer big enough to haul whatever you have plus whatever you want to get. The Pioneer is 10' machine, so if you want to carry two, you need at least a 20' trailer.
If you can find one and afford it, AND have a safe place to store it, I'd advise looking for an aluminum trailer. I lucked into a 28' tongue-pull deckover on Craigslist when I went to buy a Talon and knew I was keeping the Pioneer and Foreman. It's nice and light so it doesn't burden the truck or kill your mileage. It is also lightweight enough to help you from getting stuck in a muddy parking lot if rain hits the park you are at.