So I can't speak to all your questions. But maybe I can help a little. And your mileage may vary a little.... I'm in the PNW but on the dry side, so in general my area has an easier time of staying dry due to very little rain and low humidity. I wanted to do deep litter also, but ended up doing kind of a hybrid so that I don't have to constantly clean it out. I have lower back issues and can't deal with that kind of constant maintenance. I have 5 ducks so the amount of waste is similar to yours.
I don't actually have dirt in the coop, just straw. And there is a mix of shavings and straw in the nest boxes. I buy a product called Sweet PDZ, which is mainly to keep horse stalls fresh, but can be used for all animals. It is totally nontoxic and will not hurt your birds if they ingest it. So to start, on my bare floor (plastic), I sprinkled a nice layer of it. It's like dust. If you've ever used diatomaceous earth, it's kind of the same consistency. I sprinkled about 1/8" on the entire floor, then put a layer of straw. The PDZ seems to keep everything super dry with minimal smells. I keep a metal rake inside the coop for daily "stirring." Every few days you can use your rake to mix the poo on top with the straw, also exposing it more to the PDZ which dries it out. On about a weekly or less basic I sprinkle more straw from a bale. I occasionally will sprinkle more PDZ on top, too, if it seems a little wet. Once you have a really thick layer of straw in there, I've found that I just need to keep it turned/stirred with the rake with occasional treatment of PDZ. I got my ducks in March and have only totally cleaned out the coop once, and to be honest it was not necessary. I did it because I needed the poopy straw to use as mulch on my veggie garden (this is a GREAT use for your straw). I could probably get away with an annual clean out but will probably end up doing it twice a year because I need the straw for the garden.
Hope this helps!