Nice looking car! It should treat you well. I have driven mine, rain or shine for the past three years every day and it hasn't let me down once.
For seats, check out the E21 320is Recaro seats. They are a straight bolt in with no bracket modifications needed. I have a set that were given to me and I absolutely love them.
Small things 02 owners (some) like are side marker delete. No one likes useless trim. Aluminum radiator (however your M42 probably already has sufficient cooling). Hella H4 headlights for added night time visibility. Electronic fan (but like I said previously you're probably set). Suspension suspension suspension! Bushings, brakes, steering, tires, ect. All of those things will transform a car from feeling sloppy to extremely tight.