I would start off with a good service including Cambelt change followed by all new sensors and a set up and checkover. At least you will know where you are starting from then. I don't think it should officially pass an mot without cat, but probably ways around that. Then if all ok consider modifying after that. Then as for parts missing etc its a matter of keeping eyes open on ebay and here.
The battery light on feint all the time probably means alternator on way out but not expensive to get reconditioned. Abs sensors should be available but you need to make sure if its that causi g problem. A simple test with a multimeter will identify a knackered sensor
Hopefully a bit of time and money should see it something like. How much it costs depends how much you can do yourself.