I think resting makes more difference in an older bird as compared to a young one like yours were. I don't think you are in that much trouble but as Egghead said, let the meat rest in the fridge a day or so after it thaws. I freeze mine the same day I butcher and typically put them in the fridge on Sunday for cooking Thursday. Mine are not the Cornish X broilers but dual purpose pullets 8 months old or less or cockerels under 6 months old. I don't fry, grill, or roast mine because of their age when I butcher, instead I generally bake them at a low temperature with moisture. I've taken these to gatherings and people that don't know what our chicken is supposed to taste like have not complained at all.
Resting is about rigor mortis and letting it pass. If you cook the bird right after you butcher but before rigor mortis sets up you will be fine but if you freeze them it's probably a good idea if you let it rest, either before or after freezing.
Brining is something different. There are different ways to brine and different "recipes" if you will. It typically involves salt and water as a minimum though I've seen an article on dry brining. There is no set way to do any of this stuff, there are always variations. The salt is absorbed into the meat and affects its flavor. It also helps keep it moist. Personal preference comes into play. The saltier the brine and the longer it is soaked the more salt is absorbed the saltier the meat will be. Some people consider that a flavor enhancement, some not so much. We all have different tastes. I'd think with the moisture retention brining would be more important if you fry, grill, or roast than if you use a slower moister method of cooking.
Then you have marinating, usually using a wine or vinegar base to help tenderize the meat just before cooking. Of course you can add all kinds of different herbs, spices, or other stuff for a wide range of flavors. You don't want to marinate too long as it can make the meat a bit mushy with that acid breaking the meat down. I would not marinate before freezing. Of course you can marinate any meat for flavor but is probably more important as a tenderizing method on older birds.
I think you will be OK. Good luck.