Ok here goes something
1. Is peat moss and potting soil a good emersed substrate?
2. Will the combination above be safe for other plants and other fish and shrimp?
3. I want to grow hc, where can I get some?
1: Im finding I prefer to use a 2:1 peat and sand mix with partially submerged pots for most applications. Im currently trying peat/manure for Echinodorus since they are heavy root feeders and have not seen any signs of root burn. They are showing excellent growth as compared to straight topsoil, but that might have something to do with the IBA and NAA which I had not used with the previous media. It really seems to depend on what plant you want to grow. I have HC growing on straight peat, peat/coarse sand mix, wet nonsubmerged sphagnum in a tray, and on a piece of floating cypress that wicks water to the top and keeps it wet. The best growth seems to be on the piece of wood without any media at all. B heteroclita and Anubias v nana are also very happy there.
2: Safety would depend on what treatments have been made or what the ingredients in the mix are. Preemergent herbicides, copper, fertilizers etc. I avoid prepackaged potting soils, you never know whats in them. The closest I get is Scott's topsoil, and even thats not consistent and is mixed regionally. You might also want to avoid Miracle Gro peat, they add funny stuff. You may need to soak/flush with tapwater to raise the pH, depending on the source of the peat and whether any treatments have been done to the medium to adjust pH. Or I suppose you could just buffer the water in the basin if it is an issue. You may want to soak the peat in RO water for awhile and test the pH.
3: You mean you cant find any HC at your LFS? I always see it on AquaBid. I got mine from Aquaspot.