You're not going to get great results using a roll fed cutter. Assuming you'll be printing and cutting 30 mil, it's super heavy. Your pinch rollers will slip and it will require a great deal of babysitting. When I was cutting on a roll fed cutter, I would limit the sheet size to about 30", and would babysit the sheet through the entire cut. Even then, depending on the size of the cut, there may be some slipping. Unfortunately, on that cutter, you cannot add pinch rollers, which go a long way towards increasing accuracy.
As far as pressure, you'll need around 600-650g with a sharp 60 degree blade. On my roll cutter, 350g (the max) would cut about 1/3-1/2 of the way through, requiring folding and trimming when plucking out. I try to cut about 90% through on my flatbed so they are easier to pluck out.
I'd echo the above - either hand finish or farm them out. Unfortunately, corner rounders are also a bit pricey to buy for just one job, so depending on the size of the job, it may be best to farm them out.