I'd aim for 90C. The engine is more efficient at higher temps, better MPG, etc. My car runs at 90-95C almost all the time, which may explain the 30-32mpg I can get (with a light foot).

Definitely locate a bigger alternator. The 143A units should be the easiest to find, and a little cheaper than the 150A too. Either one is an order of magnitude improvement over the tinkertoy 70A stock item.