I dont know, I say go for it. If you have faith in your fewr factor working and your common sense, then give it a shot. Just know when to back off.
as for gear, get the cheapest possible. 60$ harness will save your life as well as a 325$ harness, just not as comfortable.
I have been thinking about this a bit because I know I got started into tree work after a big late spring storm hit denver.
I went out with a rock climbing harness, a rock rope, some slings and a friend to belay me. I used a nasty old dull macullough.
My friend belayed me as I lead climbed the tree, setting slings periodically as I went. He lowered me down to the limbs that were busted off and I lit into them with the mac.
Not safe or approved but it was fun as hell and for a couple of 17 year olds, we made a ton of money. And I'm still here climbing trees.
I also look back to climbing trees as a kid 10 or 12. We would climb 60 feet up into easy climbing trees with no ropes, nothing. Super fun, and three points of contact is safe as long as your head is functioning. what is dangerous is if you by chance faint or get vertigo.
I saw a tree house the other day that was WAY up there. my first thought was, oh my god those kids arn't even tied in! thats not ANSI approved! but hell, they are kids, I was just like them, and sure one of them will probably fall, break an arm or get a cuncusion but thats part of growing up.
so I say, go do the tree. It sounds like your looking for resources on how. take your time, practice tying your knots climbing a crabapple and have the brains to pull out if you get up there and poop your pants. Macho is the killer.
Oh, someone said that dead ash is really brittle. Thats not my experience at all. I take down a lot up here in EAB zone. I think it is pretty strong. Dead suckers snag my throw line all the time and I wish it were brittle at those times. It is stronger and safer than dead oak in my experience. The hinge wood holds real nice. Very beautiful wood, and usually simple straight foward removals. I am glad we dont have an emerald silver maple borer at any rate.
good luck