Jen-
In theory, power steering pumps should be easy to replace. Should be 3 or 4 bolts and two hoses.
But it just depends on access and if you can swing a wrench in there.
I got started on buying MBs just because of a power steering pump failure on my wife's 1992 Dodge Spirit. The car was otherwise running OK (burned oil), but I knew I would have to be doing a lot or work on that car soon. So, one day, the PS belt slipped off- I can only assume the pulley bearing was bad and the the belt would't stay on. So I looked at where the PS pump was (front wheel drive v-6 Mitsubishi engine)-
back up against the firewall under the back bank of cylinders. I didn't want to deal with it so I got rid of it and started buying W123s.
Minivan might well be a problem.
Rick