newbie needs help

Hi Guys and Girls:
I am in the process of buying my first RZR. I plan to buy a used machine, probably an 800CC or 900CC.
My 18 year old nephew and my 65 year old wife both plan to drive it so I can see differing driving styles. I live in Ontario Canada but we’ll keep the machine in the BC mountains (semi arid climate but lots of rivers/creeks/etc).
I see lots for sale and I wonder what I should look for.
So, here are a couple of questions for you.
1. Suspension. Are the stock components satisfactory or should I upgrade?
2. Mud bogging…I see some machines advertised as "never mud bogged". I assume mud bogging creates extra stress on the machine so that is something I want to avoid?
3. Engine and drivetrain. Anything I should look for?
Any advice would be greatly appreciated.
Thanks in advance Doug