Newbie here....

I recentely bought a 1990 325 ix 5 speed as beater car for getting back and forth from work...especially for when the snows start falling here in Bavaria.

The vehicle is euro spec with 161XXX km  (100,XXX miles) on it.  The only real problems is that it has some rust damage on the outside from 16 years of Bavarian winters, and the interior is definitely showing its age.  Otherwise the engine is strong, and I would like to keep it that way.  What are somethings I might want to look at in regards to maintenance and upkeep?

I bought the vehicle for $1000 out the door, and I know little about its history except that the breaks were replaced a year ago, and I have since changed the oil.

I have read that I may need to replace the timing belt (since it is a belt and not a chain), and I already planned on installing new spark plugs.  I would like to know if there is anything else I should consider doing to keep the engine healthy, and maybe restore some of its vitality.  New air filter maybe?  Perhaps a new fuel filter?  I am not too familiar with BMWs and I don't know where their weak links are so to speak.

I'm also not really looking for much of a performance boost, unless it is something cheap and/or the work needed to be done anyway. For example, I've read new and larger fuel injectors could go a long way to boost performance especially in the top end.

I am also looking to possibly increase fuel efficiency as well.  So far I am getting just shy of 23mpg on 80% highway driving (I drive this car conservatively) Maybe 23 mph is good for this car...I just  don't know, but I expected a little better from a 6 cylinder on mostly highway driving.

Also I have a standard 5 speed tranny....does anyone happen to know what the gear ratios for the transmission are, and what the final drive ratio is for my car?

Your help is appreciated.......