1) Do you 'need' a Belt Mountain Base pin (running into problems with the base pin jumping)? Or just want one.... At any rate. I don't use the allen screw at all. I just leave it be on my #5 base pins. No need to to 'drill' anything. Also you have a 3 3/4 in barrel. First the pin is just a New Vaquero (medium frame) base pin. BUT, with the short barrel, you need a 'small' head on the base pin to allow the ejector rod to properly eject the shells. You shouldn't use therefore a #5 base pin for the shorty. Hope that kind of makes since! Kyle will sell you the right one if you ask
2) I personally just clean my guns with Hoppes #9 and that is that (blued and SS) Sometimes I'll lightly oil the gun if put away for a few months. Not a big deal here. Never have seen any 'rusting'.
3) First thing I do is break my Rugers all the way down and thoroughly clean them. Then oil and good to go.
4) Never happen. You are good for several life times of shooting. Just go shoot it and enjoy.