am i missing something here but isnt he asking whats the best way with the stuff hes got or could reasonable hire and still make money on the job. not sure how densely populated the land is with tress but he mentioned having to leave anything over 8" so crashing through the area with a track loader raking or huge mulcher or m1 abrahams isn't really practical.
personally id be knocking over and pulling out the smaller tress with a midi 5-8ton and stacking behind me as i went to be carried out by what you have with a grapple or can skid out with a chain be it an horse
, atv, skid/ctl/telehandler or backhoe to the shredder. buck anything to long at the back on the excavator and carry it out of there.
we tend to use the mechanical advantage of the tree against itself when using smaller machines, dig a bit out the back them use the tree as a lever to push it over and pull the stump at the same time.