U don't say wot size the stems are u want to chip? Or wot they look like how bushy etc for fitting down the chute of chipper.
Most hire chippers are 6" ish size at normal hire places, more specialist might have bigger 1s. Is road tow OK or need a tracked version??
Really all the big makes are pretty good.
If u have never used a chipper before watch which way the blade spins as will throw wood to that side, can catch ur hand a sore q against chute sides and watch any diagonal cuts to put long face down as will flip up and sideways.
Seen a few sore chins and noses and helmets knocked off with them
Dunno how ur thinking off cutting it??
Sometimes not that easy getting at it.
I imagine will be a pain to hand cut as probably be wide and saw above ur head all day has safety issues, plus the dragging offhawthorn or black thorn can be a real bugger.
Buy a set of welding guantlets for handling the thorn
It's becoming more and more common to do jobs like that mechanically with a digger and tree shear attachment feeding direct into a chipper.
Won't be cheap but will do it in no time and no infected hands from blackthorn.