Wot jagarr says above is good advice, a decent brush cutter will handle a lot of that very easily. Seen my felling 6" 20 or 30ft tall birch with mine with a saw blade on, not ideal but doable.
If u have a brair/bramble problem the mulcher/shredder blades are an absolute game changer, the curved ends make a massive difference.
1 thing i will say 1/2 acre is not that big ( roughly half a fitba pitch)
U say its very productive as it is, well for stalking.
If it aibt broke dont try to fix it.
Wot is ur actually long term aim?
If its to maximise stalking it sounds like it already is pretty good habitat.
Depends wot u end up doing but often 'tidying' a wood can have a negative effect on wildlife habitat.
Just saying just be careful u could make it worse thinking ur inproving it.
It sounds luje nych of ur woodland is coplice so wotever u do in a few years it will grow back.