The biggest issue I would be concerned about is the speedo. Mostly because if it is intermittently not working.. then it may also intermittently not be counting miles. Also if it is a faulty cluster then you will be looking at a hefty price to replace the M specific instrument cluster which costs more than the non-M version. I would at the very minimum run a carfax on the car and try to determine if the reported miles goes in line with what the Carfax reports shows.
The next item: Drivers seat torn. if its just a small tear or cracking then it can probably be repaired by a mobile upholstery repair guy fairly cheap. If it has large tears and you need to replace the leather or the seat itself you will find that it costs a fortune. Leather upholstery work is not cheap especially when you have a seat with custom m flags woven in to the leather.
My opinion on aftermarket "racing" seats: fugly
Next issue AC: if the blower fan is shutting off intermittently then it could be a few different things.
1) faulty blower fan itself about $450 or so to replace
2) faulty blower resistor/final stage $1-200 to replace
3) faulty control module (IHKA) $4-500
(all ballpark prices)
Last item Tires and Alignment: Tires-depends on brand etc
Alignment- Best to have done at a dealer who will load the car down with the proper weight and measure the ride height which is vital to get the correct specs. $180-200
beyond that it may need front end bushings or control arms or other suspension components in order to properly align it especially with 100k miles (possibly 140k if the speedo hasnt worked for 2 years)
My opinion: Sounds like the owner is trying to dump a money pit. If you can do a lot of the work yourself and have connections for getting parts cheap or a good local BMWjunkyard then it may be worth buying PROVIDED that you can get a realistic idea of the true mileage of the vehicle.
If you are a guy who will have to take it to a shop and pay retail for all of this then I'd pass.