I see you will get a LOT of concerned people responding on this thread. However; I feel that if you are going to get in the bucket and trim trees, this is a safer alternative. It looks as though you have put some thought into your project for sure. Just as a bit of added safety I would slap some ratchet straps on the outside edges help secure it within the bucket.
You seem handy with wood. Just a suggestion, but you could fab some sort of ladder with a platform and attach it to your 3pt hitch and transport it as such. Think of it as a "portable fixed scaffold" in a manner of speaking.
I will confess that I am also guilty of climbing in the bucket to get to those hard-to-reach limbs. I am even stupid enough to let my teen aged son work the loader while I am in it. I can see a, "mischievous look in his eyes" when he touches the loader controls. Yep I am looking for a death sentence....from that boy!!
Safety is a big deal; but I was raised doing things that should have killed me. Yep, I was one of those kids that loved to ride in the bed of the truck running 70mph down the Interstate. Waving at a "Cop with no seatbelt on" pass us in the fast lane- Chips Patrol just started on TV and I was a fan.
Somehow...... I am still here.