I would still maybe try and get a skid steer in with a cutting head into the sections you can, it gets a LOT of work done without killing your back, the rest??
yrs back I would have suggested maybe try and find some younger kids willing to work, and hire them to do selective trimming for you ( I used to spray paint things i wanted cut and removed and had kids do work for c ash)
but these day's, kids don;t like doing manual labor much and if they did the costs wouldn;t be any cheaper than hiring a professional to do it, sadly, kids ain;'t the same as they once were in most places any how, too many spoiled one if you ask me!
that said, if you don't have maybe invest in a good brush trimmer, and use that to be more selective
time consuming, cutting and stacking, but will help get rid of a bunch, but key on many of the things you want gone will be following up on cuttings with spraying before they make new berry's and seeds
as that's the killer on them things, birds eat em and crap em out all over making things spread
took me several yrs to get a 20 acres section working alone, but in the end I was very happy I spent the time stacking and burning piles
in winter time with snow down I will admit I did get a little help now and then from my sisters smaller kids, as I would let them have cook outs in the snow which helped lure them into some work , plus kids seemed to like building fires and adding wood to them L, would; even try and get them a l;ittle extra motivated by making games of it, as to who could build the biggest pile and such, LOL
but kids will be kids, enthusiasm doesn't last all day long that's for sure, but hey, they had fun and I got some help, so win win, got to take them as they come some times!
AT hunting camp, we make it more of a work deal, where members HAVE to put in X amount of time, in order to hunt the following yr, so that works too maybe if you let others hunt your land!
but could be some idea's for you on how to get some help!