I use the same thread that I've always used since I started sewing- Gutermann. I've tried Coats & Clark, but it seems like I always get tension problems when I use that thread. I've heard their newer thread spools are better and people seem to like it now, but I haven't tried it yet.
I've used Mettler here and there without problems, but can't afford to buy it all the time.
You'll love your machine. I just got a zigzag attachment for mine and was afraid to use it because I heard they don't work well, but I was pleasantly surprised. I made this outfit last night and had no problems with the applique on a thin t-shirt:
Good luck and I know you'll love it!