I guess first you are going to have to set some goals and plan around them.
Are you looking at full time living in the 5er? Will you also go "home" for several months and then hit the road for just a couple months at a time?
Do you have a specific budget you are trying to stay within?
Are you looking at Boondocking or staying in developed campgrounds?
Are you planning on going to a single destination for months at a time, or travelling frequently?
How much experience do you have with towing?
Are you fairly self sufficient as far as maintenance and repairs, or will you be seeking hired assistance?
Think through all these questions and then narrowing your choices will become a little easier.
Happy Motoring