You usually own the pipe after the meter. The utility's shutoff often requires a special tool to turn it off (if that leaks, it's usually their problem). So, it's hard to say, not knowing which valve you shut off. replacing you main shutoff usually requires shutting the city's valve off so you can install or repair yours to fix the problem. There are ways around that, but each situation is different.
Also, not knowing what brand and model of shower valve you have makes only generic help, and may not be what you need.
On many shower valves, the entire guts of the valve is in a cartridge, so replacing it often solves many wear problems. But, some are rebuildable, and don't have a cartridge...a picture would help clear this up and get you better help.