Need to knows when buying

[oday]

hi guys new to the site, names josh live in s.a, yes im young only 24 but have a good job and appreciate good cars. Now im lookingatthe x5's been looking at the 01 to 03 e53 range, v8's. Been looking on the site and from what i can gather these models have a few problems with the transmissions, is this correct? What other problems am i likely to have looking to spend around the 20,000 to 25,000 mark. Aslo gathering that alot of the problems dissapear from the 04 model on? What year does the shape change in them because from what ive seen the net the 04 is a slighty diff shape is this correct? They main thin i will be using it for is to tow my ski boat that weighs around 2100kgs on the trailer. Also have come from the modding backround so what mods are available? Chip ecu, zorst, bigger brakes, cams? Any help is much appreciated thanks guys