welcome to the forums.
First of all, like any 16 year old car reliability is going to be a factor. Its an older car, and things have to be replaced. I own a 1991 E30 and if i dont stay on top of regular maintenace things tend to break. Of course compared to almost any other car manufacturer an E30 is reliable for its age.
If you get one consider changing the thermostat, belts, water pump right off the bat just to be safe. They tend to go out around 100k miles.
There are three point seta belts in the back of my 318. Except the middle seat, where there is just a lap belt.
Well hope that answered ur questions. I think you will be pleased with an E30, they are great cars. Good luck.
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