Greydog

Hi Kirk
Welcome to the Forum
If I recall they have the same spigot ring size so should be OK I take it when you say mixed size you mean wider rear wheels than front ? If the 118d is front or rear wheel drive then wheels/tyres are cosmetic. The X drive cars need wheels and tyres that are matched rolling radius or drive train damage will happen quickly
Dave

Morning Gary
Is the clutch on the compressor kicking in and out ? Fuses OK ? Really daft one is the drive belt OK ? As already said it could be the Dryer
If the system is charged and Drive belt Fuses and Compressor clutch are OK then a diagnostic scan needs to be carried out
Dave

First check the solenoid is getting power (test lamp or multi meter) if it is you will need to remove the starter in order to bench test it
On the bench make sure the pinion gear is free and moving in its slides you will need a spare battery to test the motor (make sure it's secure in a bench vise. Connect positive to the solenoid and touch the negative lead to the starter body it should spin if not then it looks like a new starter
Dave

Hi Joe
I change Vac lines and breather hoses as a service item on our cars 2 X5's and Wife's Subaru Outback all are serviced annually to manufacturers standards by myself (son says I have OCD 🤣) any rubber hoses showing signs of degrading are changed as a matter of course so I wouldn't worry as long as its changed. Oil and rubber are not best friends and as your potential purchase is around 7 years old it is quite likely near end of service.
Subaru is a 2004 3.0 has 164k on the clock and runs like a Swiss watch BMW E53 4.6is 137k like the Subaru runs really well BMW E70 3.0d 138k as the other two.
Dave