While I cannot speak to everything here I can add a bit to the conversation.
On the frog/toad laying there is not really much more you can do than provide them with plenty of habitat. Obviously the more habitat you provide the better for your purposes. I suppose you might find a
local variety that was not protected and try breeding them to release at different times of the year, but most frogs need specific cycles of light and dark as well as cooling and heating to trigger reproduction.
Most water fowl tend towards the smaller aquatic snails, larger ones like the
apple snail have pretty tough shells. Some form of fish perhaps, carp or koi; both would help control algae and weeds and be a good source of protein.
For a simple
sustainable protein especially for
chickens look into what reptile breeders and hobbyists are doing. You actually have a lot of choices there, some of those are crickets, meal worms, and cockroaches. This is where you can get creative, find one of your local species of insects and go for it.
One observation: I have noticed a lot of people who must lock up their chickens at night often do not let their chickens out at or just before sunrise and often have them locked up before sunset, I think that is a mistake. The majority of insects and wildlife in general are most active at those times.
So having said all that I think the easiest thing to do would be what you plan to do already; observe and then use those observations to create areas that help benefit the natural production of the types of protein already in your area. I would look for beneficial insects that are already being eating by your other animals and see what could be done to help increase their populations. Generally providing habitat is all that is necessary.
This is one of those scenarios actually that gets better through the use of
permaculture as a whole without the need to hyper focus on specifically breeding insects for food. By simply planting diverse and complex plant guilds that are in tune with the natural cycles in your area and leaving some areas more wild than others the insects will come on their own as you are now already providing them with food and habitat.
Jeff