Hi, I would recommend two books, Jeff Jepson's "the Tree Climber's Companion" and Gerald Beranek's "The Fundamentals of General Tree Work". Both are well written and easy to read. Both are very informative. Must have reading for this business. Both may be had at a number of places that specalize in this business- Wesspur is a good company to try.
In answer to your questions the aluminum gaffs have steel gaffs, its the J part that is aluminum. No, a linesman's belt is not correct for this work nor are lineman's spikes. And no, I would not buy used equipment. I have been advised that dropping either the spikes or the belt from any distance onto a hard surface, like a concrete driveway, can crack the metal. This may be found by magnafluxing and I was advised to have my equipment, spurs and belt, magnafluxed every year. Spurs as others have said, are only used for removals. Palm trees I don't know anything about, but you being in Florida they (the palm trees) may have a different approach.
Others have written about how this is a dangerous business and perhaps they got your back up a bit. They are only trying to keep you alive and well.
You mention ladders and then mention them again. Eeek. Topping a tree is like cutting one down on the ground except there is nowhere to run. As the top comes out it pushes against the spar. It pushes hard. This make the spar move away from the direction of fall of the top. Every time you are tied in to a spar and cut the top out you really do a dance up there sometimes the arc of the swing is many feet. If you are on a ladder the top of the ladder will either swing with the spar --or it will not and you and the ladder and the chainsaw will fall. There about a thousand other things that can happen wrong, but I mention only the movement of the spar when the top comes out as it seems to me to be not well understood; laypeople seem to think the spar is going to just stand there and not move an inch when the top comes out.
I hope this helps you.
Eljefe