Agree with the other comments, but with regards to the subframe you mentioned - in stock form these cars do not really crack there. Also, with the car having 18K miles - I doubt that is an issue.
Regarding the cooling system, go to a good BMW indy shop (that works on these cars) to do the PPI and they should be able to tell if anything is cracking/dry due to age; may need to replace the upper and lower hoses and possibly tires if they are old.
At 18K miles your suspension should be perfectly fine unless your father went off-roading daily with it.
Check the sunroof drains, make sure they are fine and not clogged - the indy shop should be able to shoot pressurized air through them either way to loosen any debris that would be stuck.
Also, the vanos rarely go wrong on these cars, that is more of an issue with the s54 motors.
I think BAT is the way to go with the type of car you are describing.
2003 330i ZHP; Imola/Alcantara 6 speed, 2002 330xi ZSP; Blue gray/Black 5 speed