Dave H
If using open dishes, your birds are probably going to nest in them. This isn't an issue if you only have males, but if one or both of them are female, it could encourage laying and increase the risk of egg-binding. I transitioned my birds to a gravity/hopper feeder to start, as the opening was not large enough to nest in. It took them several days to use the new feeders, so I had to leave the old ones in for a bit. Gravity feeders also tend to get soiled less, although if you use a gravity feeder for water, they will need a dish for bathing a few times a week. The water container I have now is covered and allows bathing, but I had to modify a hummingbird feeder to make it.
My society finches used to eat the dry eggfood plain, but went off it after I started giving them plain cooked egg. If they'll eat it dry, I'd recommend leaving it dry since it'll stay good for months. I feed egg every day during breeding season, never during a 2-4 week winter austerity diet, and 2-4 times a week otherwise.
As for seed, mine like millet, buckwheat, canary grass, oats, amaranth, sunflower chips, sesame, and dry corn. When using a food dish I feed the first four separately and occasionally supplement it with the others. The seed system I use now might not work for you; the my cage substrate is sand with a layer of dry leaves, and I throw the 8-seed mix on the bottom for them to forage for, away from the area where they usually poop. They spend a few hours a day looking for the seed. However, my first birds were dumb as dirt and probably would have starved before they figured out how to eat on the floor. Plus, you'd have to make a foraging tray if your cage bottom isn't solid with a wide lip.
I feed veggies and egg in the morning and leave it in a flat dish all day. They usually eat it all or ignore it after a couple of hours. I'm trying to add sprouted seed to their diet, as well.
They also have ground oyster shell, charcoal, and salt free-choice in separate containers. Switching a mineral-deprived bird to free-choice minerals can be risky, as they may overeat. Otherwise, free-choice minerals in separate dishes should work well. I don't use vitamins, although I did mix a bit of spirulina in their eggfood once while they moulted. They liked it, but it wasn't necessary.