Maisiesdad Welcome to the club to answer your questions very briefly, budget, power and physical size will determine the model you will want. In my opinion a u1600 214hp is the best power and weight machine and fetch top money, or at the other end a u1000 ag.
Regarding things that can go wrong all depends on the life it's had and how well it's been looked after not how old it is,main things cab rot, hubs, gearbox below 6/7000 hrs after that engine again depends how it's been looked after, when looking allways find one with the spec you want as retro fitting is expensive.
We have a 411 that we are doing up for a customer that has no spec so was resenalable money he likes it that way and only wants it as a toy to drive round in so suits him.
If I come across anything I'll let you know
Moose