First of all, really nice work.
Second of all, please at least replace the waterpump and explosion tank. You should be able to tell if the radiator hoses are good or not, mine were fine when I replaced my set up. I replaced the upper hose simply because I had it off the car anyway, the lower is such a bastard to get off that I left it on there. You can replace the thermostat too in order to save yourself having to drain the system twice when it goes (mine went at ~110k).
Third, have you checked for any oil leaks? With the condition of the rest of the car, it wouldn't surprise me in the least to find that the valve cover and oil filter housing gaskets shot. Also, change the oil and all drive line fluids before you drive it any more.
Lastly, the reason all this stuff fails at 100k is that is the expected life of the components in your car. The new ones will last for another 100k before they also poop out. Except for the brakes obviously.
Welcome to BMW ownership!