The most I've done in a day is 4-5, I don't have an automatic plucker.
Most folks put them in a cooler on ice to cool them down before they go in the fridge - that's what I do. I butcher, skin or pluck, eviscerate, then cut up or not, put bird or parted bird on a 2-4" layer of ice in a cooler, and cover with 2-4" of ice. Chicken is placed in bags and no more than 2-4" thick, or a carcass covered with thicker ice. It takes about 2 hours to cool the carcass or parted bird. If more than one or two go straight into the fridge, it warms up the fridge too much, and they don't get cold quickly enough to prevent bacteria. You would have to lay it out (not stack the chicken) so they get as much fridge air as possible. I've done that and it was fine, but the cooler is a more certain choice for quick cool down, and better for more than one or two birds at a time.
What exactly was the state of the birds when you put them in the fridge? Gut still in? Feathers and skin still on? Drained of blood? Were they soaked in water?
If the guts are still in, freezer like you did was probably the way to go - it will get them cold faster. Like previous poster said, whole game birds used to be stored with guts in around 50F, for a day or so before gutting/plucking, but I never got a good answer if folks only ate the breast meat afterwards, or actually did gut afterwards, so I haven't done that.
If you put the whole bird in the freezer, and gut afterwards, and it smells fine, then I"d stick with what works for you. To combat the toughness, once it's been cleaned (gutted/skinned) and possibly parted out, put the bird in the fridge for ~3-5 days to rest. Resting can happen before or after freezing. Test the bird after resting to see if rigor has passed by moving a leg joint and seeing if it moves easily. Rest the bird until rigor has passed. There should be no bad smell this whole time.
Cook the bird at 275F in a covered dutch oven, or in the oven uncovered if you have skin on, or put cheese or sauce on the skinless breasts to retain moisture, etc. for 2-4 hours until internal temperature of the thickest meat is at least 175F. I like to cook to 180-185F. The meat should fall off the bone when you're done. If it doesn't, with your next bird of the same age, pressure cook it. A whole carcass can be pressure cooked. Tender meat guaranteed. I've done 1 yr old rooster in a pressure cooker, tender like anything. Good for chicken salad or sandwiches, and the broth makes great stock.
Good luck! Don't give up, I think you're almost there!
I have killed some before but cleaned them and put them in the freezer right away. They only smelled when I broke the intestines on accident but the meat was unbelievably tough and then I read about letting the meat rest and some people said then let it rest 4-5 hours to 2 days before they even clean it just cool it down. So I decided to try that 
And idk if your meat is totally ruined this time. Listen to others on here who have experience with that. I'm just making a suggestion for next time.
