Welcome to the fold Bonnevillet140v.
Nice choice of machines, we just don't mention the word BMW on this forum unless we are bagging them
or Harleys.
The 01 ST's are a great machine and some guys on the forum have very high (80,000K's and higher) mileage on them.
The 01's were the last of the "older" 955i motors. The 02 onwards had the alternator on the other side which reduced noise and they had slightly more ponies.
They are an excellent real world machine overall. No major issues but check for regular maintenance as you would for any machine!!
Oil and filters are easy with the oil filter tool (I picked one up for $16AUD -6 pounds!!) otherwise you have to stick a screw driver through the side of the filter

to get it off!!
They have heaps of torque (pull from 2,000rpm) and great top end (240kph) speed on the motorways.
As I said "excellent real world machine". Good luck with the possible purchase