RE: Treestands?
Cowboy
Outfitters up here use wood tree stands like you want to build all the time
15-20+ up
wooden ladders made of 2x4 or trees
planking for the decking
YES the stand is going to need to be checked over very carefully each year
I would even go one step further and put chain up around each support brace and lag bolted into the tree so if a screw or 2 let's go on one side then chain will not let the brace collapse
I have even thought of making one that is floating like above with only the chain holding the braces so the platform does move with the tree movement. Know what im saying?