(1) No, the view through the viewfinder should not be blue or purple, it should be clear. Were you wearing polarizing glasses?
(2) To check the RF calibration, you first need a lens. With that mounted, you can open the back, put a piece of ground glass (or vellum) where the film plane would be, and fire the shutter on bulb. (the mamiya RFs will fire with the back open) Compare the sharpness of the ground glass image to what you expect from the focusing mechanism. Repeat this for close and far focus with all lenses. You'll want to do this test on a tripod.
(3) If the VF is a bit loose it can be an issue; also if the patch screen is loose (not the VF you look through but the one beside it which brings in the light for the VF patch) then that is a problem too. Both should be fairly easy to remedy but you don't want to buy something problematic, especially when so many excellent conditions cameras are available at quite low cost.
(4) You can fire the lens with the back open as I described and check out speeds etc. and also put some film through it and check that the take-up mechanism is working properly and winding tightly.
It's a superb camera system, however you may wish to find a nearby apugger with a bit more experience to check it out for you, especially since you are new to RFs. Otherwise just make sure you've got a good return policy and shoot some film!