Glad you joined the fun. Be sure to post some pictures of your wood find. The TRA001 is a terrific machine, lots of power. To flatten stuff with a router generally requires a router sled, which holds the router mounted on two steel rods, secured to two end pieces. You're going to use a fairly large bit that leaves a flat surface. That would be to work the stock down to the thickness you want to work with. Here's a picture of a router sled. I think I'd probably apply some friction-free tape on the aluminum to make it slide easier.
On twisted or irregular pieces, you will sometimes be propping up low corners with the stock on a carrier. That is also a method for turning a planer into an upside-down jointer. Don't try to take very much wood off on any one pass. An eighth of an inch is ample
The more I do, the less I accomplish.