I've got a silver maple that was girdled by deer this spring. It hasn't actually died, but it grew new branches from below the damage, and is quite an unattractive tree now. So I plan to propagate some new ones off this tree, and then get rid of the damaged parent tree. Here is my question:

What tecnique will I likely have the best luck with? So far I've started 8 cuttings; some are just softwood, some are softwood with a old wood "heel" on them. I'm just sort of trying whatever and seeing what works. I've got them planted in pots 75% perlite/25% peat moss, covered in clear plastic(which I'll remove a couple times a day), on a heat mat and with artifical lights on them because I don't have a good area with bright but indirect sun. I'm misting them a couple times a day and keeping the soil wet for now. They were dipped in rooting hormone before planting, and are about 6 in total length, though most of that is buried. I also tried scraping some of them on one side of the buried stem for more area for roots. As you can tell, I'm not entirely sure what I'm doing and I'm just trying a bunch of different stuff! Is it better to not use a heat mat?

Would I have better luck with air layering?

Can I plant any cuttings straight into the ground outside, rather than starting them in pots, or will they die for sure?