If you have fine, low-med density hair I would use the mousse and set only once per week. Since you have the rollers already just buy the clips, I've never use the rollers with the two pieces before but it seems like those would not allow for a tighter roll to straighten your new growth but I'm not 100% sure though. Oh and buy a seamless rattail comb, those plastic seams on the cheap combs will rip through your hair delicate wet hair.
I would also suggest watching YouTube videos to see how others rollerset and choose a method that would be best for you. Also, pay attention to roller placement and how you want your finished outcome to look. It's going to take quite a few tries before you get it right but you'll get there...don't give up. I still haven't mastered Rollersetting and still get confused but I'm a lot better than I was when I began. I realized that I get my best curly sets when I do the mohawk method; rolling the center pieces toward the back and the side pieces under. I have a long head so I don't want volume on on either top or sides of my head.
If you want to wear your hair full and straight go for the roller size that will allow you to wrap your hair around the roller 1-3 times. If you like lots of curls then naturally you would go smaller, the smaller the roller the tighter the curl. Personally I would begin with the larger rollers to get the hang of it, the smaller rollers take more time and patience.
Another thing, you might want to start light handed with you products to see how your hair responds to them. Gradually increasing if you find you didn't use enough until you get a great set. Using too much of heavy products will take longer to dry and your set will come out stiff and oily. I use my leave-in, setting foam and serum and I'm good because I'm light handed and my products aren't heavy. Less is best. Good luck and please post pics so we can see how you did
.
Sent from my iPhone using LHCF