I think you're doing fine. I remember I had the EXACT same questions when I first started Thunder.. I took it slow, a ride a week maybe, and then stepped it up a little bit. I really depends on your timeline goal. For me it was I wanted him to be pretty good on trails by summer. Because I knew that he was mentally and physically ready for it, I started pushing it a little more. I just recently had the vet out for a check up and he said I don't work him enough (1-2 a week and almost never into a sweat) because he had so much soft muscle and a layer of fat over it, and it was a bit much for a 3 year old he said... so now I need to step it up again. he's ready for some real training now, I just need to do it.
Since you know your girls so well, just wait til you feel they are in a good spot to move forward and try something new. I learned to back up after a few rides. It's really simple, just sat deep, and brought my hands into my belly button and he backed. At first it was a little confusing and he resisted, but then put it together and got it at the first try. Plus since you have done so much ground work, you have that on your side. As far as the reins go, I personally just tie off the lead and just use the reins, but then have the lead line after I get off so I'm not yanking on the bit from the ground. We actually just started riding without it every once in a while. So I guess ultimately, what is your goal for them and how far would you like them to be by when? that will set if you're behind or not. If it doesnt matter when they are broke, then maybe set small goals, like by this date, I would like to have them learn to back. Horses learn so fast, most simple things that have already been imprinted don't take more than a lesson or two to figure out, and then it's just practice from there. And once they learn those simple things, you can add to it like using those cues and tools in different situations, like going in between poles set up like this l l and over logs and being on their back while re-despooking. Your doing great and all your feelings are natural. Sorry for the book!!!