Good job! Those chickens look awesome!
First time you do it is usually a bit hard for many folks.
Yours are only 3 months old, which is young actually, they can be cooked any way you like. FYI, heritage birds are usually processed anywhere from 4-6 months old, best cooking methods depend on the age of the bird.
Let them rest in the fridge until rigor passes. Could be 1-3 days, longer for older birds. Try to move the leg joint right now, and see how stiff it is. When it moves perfectly easily like grocery store chicken you know resting is done, and it's ready to freeze or cook. If you want to season it or brine it, you can take a few days to do that after the bird rests. How long it lasts in the fridge depends on how cleanly you butchered it. As long as there are no off smells, you're good.
Butchering yourself is usually cleaner than commercial operations as long as you rinse everything well and often, and keep surfaces, hands, and tools as clean as possible. Also, evisceration and chilling asap after butchering is key to minimize bacterial growth.
If you do a lot of chickens, make sure to layer ice between them when chilling them in a cooler before you put them in the fridge for aging. (Or you can age in the coolers.) You don't want a pile of chickens that retain body heat. Also, too many chickens can overwhelm the cooling capability of your fridge, but one or two is probably fine, as long as you put them in there separately, not stacked together, so they can get good chilling.
Also, you can age (rest) the bird before or after freezing. Just make sure it ages in the fridge before you cook it, so it won't be tough and stringy/inedible.
Enjoy your delicious chicken!