Here are your answers:
1: string tension - if you aren't already, consider lower tension strings as rics were designed for. I play rics almost exclusively and have for a long time - i've landed on .43-.100 ti jazz flats for all of mine. If you like rounds, try a gauge down.
2: no, unless you didn't like the stock one to begin with and/or aren't getting good break angle and/or there is 1/4" or more lift, which risks snapping the tailpiece off (this only really happens on the old cast ones which never really lift and very rarely snap but i have seen it) Less than that is considered normal but it can drive folks crazy.
3: yes - ric sells replacement bridges that have been redesigned to avoid lift and are alittle friendlier to adjust. Only a few extra holes have to be made and it is aesthetically similar to the original. Hipshot makes a popular replacement, nice high mass though i am not too fond of them for many reasons (wiggly pokey saddles that dont often go low enough). This would be a drop in but two extra holes would be needed since c64s had only a 3 screw tailpiece and the hipshot is designed to cooperate with the standard 5 hole pattern. Its footprint is similar to stock. My personal favourite is the schaller roller bridge but this requires that the hole under the bridge be filled to work properly and few are bold enough to do that. It pretty well needs a complete re-drill, too, but once you've done it, if you're anything like me, will be pleasantly surprised at the improvement.
Hope that's helpful and best of luck!
