When Should You Replace a Timing Belt, and Who Should do it?

How often should you replace a timing belt on a 1986 528e? We're owners #3, it appears that the factory belt was replaced at approximately 7 years and 66,000 miles, and that one was replaced seven years and 51,000 miles later. Belt #3, then, would be be 4.5 years old with less than 28,000 miles on it. I'm a little leery of trusting the shops' recommendations, and they also want to add a lot of things like replacing the camshaft seal and even the water pump (which was replaced with the last timing belt). We're in South Alexandria and prefer not to drive all over creation, what can you recommend, and who do you recommend do it? We really don't want someone who will tear up more than they fix. We're really gun shy of shops, and try to do any work that we can do ourselves (our cars have never run better), but this is more than we can tackle without a garage.