I wouldn't start single speeding your bike, that way you'll have a bike you can ride long distances in the future.
As for mod, stock and 24", really it would be best to try them. Try and get in contact with someone from around your area on here and see if you can join a ride and try some out. I assumed since I learned on a MTB I should get stock so did. But now, almost two years later, I think I could have got on fine and maybe improved faster. 24" I don't think are supposed to be too good for learning the basics but each to their own.
Also for your third backhop video, your pushing forward to try and lift the back wheel. Instead try keeping your body more still in a sitting position and just lift your body up and bend your knees a bit to lift the wheel. It's hard to put into writing