They are not as bad as the Cornish Cross but they will overeat. Do you plan to free range or keep them in a run? After about 3weeks I start limiting their food a bit, before that I let them eat as they want.begin putting mine out in a run (depending on weather) at 3weeks and let them root for food there. Then by 4 weeks I keep them in the run and only feed mine twice a day as much as they can eat in about 15 min. My run moves so I make sure they get new area to root. By 6weeks i let them free range and may only feed them in the morning as much as they can eat in 15 min.
You do not have to be quite as strict as you do with the Cornish Cross and they will be more active willingly. But the more you can allow them to move the healthier they will be.
Mostly in a new run, there are a lot of foxes this spring! limited free ranging when I can supervise. They are in a 10'x 20' hoop coop now, and have access to half of it. They are enjoying eating the grass/clover/weeds/etc.
Thanks for the advice on feeding them - there is a lot of info about cornish but not so much about the red rangers. They have free access to feed now, and I think I will follow your lead and let them feed twice a day when they are a bit older.