You're going to love those GGs. I've been using them for 6-7 years now, first on an old Traeger 125, then for my Weber Performer and now for my YS-640.
Re seasoning...I tried the seasoning route with the first set, and found out they'll season just fine on their own through use. They get so hot, they'll burn off any oil you put on them. What I did with subsequent sets was use a little extra oil on the meat/veggies for the first few cooks. The GGs will develop a nice gold patina after awhile.
Re cleaning...Most of the time, just run the sporkula (I think they call it the Grate Tool, the spatula/fork thingy) upside down through the troughs after each cook to clean the gunk out. After about 5 years of use, I had a brain fart and decided to throw them in my convection oven on self-clean. That worked GREAT! Well, EXCEPT for one little thing...the cleaning generated a LOT, I mean a LOT of smoke. If I didn't have a "vented to the outside" OTR hood, I'd have set off every smoke detector in the house. The inside of my oven now has that same gold patina as the GGs.
Silly me.:roll:
Edit: Also, don't be afraid to use them rail-side down. The bottom flat surface make a great griddle for things like burgers.