Welcome to the website.
I am not one to recommend used equipment unless you know the person you are purchasing from - otherwise - you are probably just purchasing someone else's problems. Yet, you seem happy with used equipment so you might consider finding a computer recycler who will help you. I would greatly be concerned about technical support of the system after your purchase. As a final thought, you might consider emailing
fpcinfo@fujitsupc.com and asking about the systems. If you are interested in the 3500 then make sure you consider the outdoor screens.
Best of luck.