AHH, the HOA, too bad.
If it was not for them you could still plant on the
fence line and prune the half that goes over into your neighbors yard, a living
fence or quasi-espalier style.
As for the steepness you could use some wood/stone or something to hold it up untill some grass/root take over and hold the soil.
If you have 30ft between the tree and your house/foundation I say go for the pecan tree otherwise I would be cautious.
If all you are doing is digging a 3ft deep and wide hole and then adding 1inch of compost per month then I dont see a big problem.
However please be mindful that if you add dirt/compost/etc to the hole it will be rootbound, only expanding an additional feet or so.
And while 3-4ft might be enough for a 8-10ft tree (think container plant) it will not be enough for a 30-50ft tree.
Maybe you dont even have 1ft of soil all you have is bedrock/clay.
If that is the case you are just going to have to import that 1ft+ of soil
But with the steepness you are going to have to add it inch by inch giving the grass/plant
root time to colonize and hold it.
Its only after this is done that you will be able to plant your trees.