BudDawg, I have a 3520 and use a 6 footer for field mowing and minor brush control with no problems. If I had a 4520, I would get either a really heavy duty 6 footer or a medium duty 7 footer.
A 5 footer is too narrow and won't cover your track.
Don't worry about the PTO or the 3 point hitch. They are built for this sort of work.