About valet

1 - What happens when I "valet install" on a machine that valet is already running? is the answer the same about all packages and programs?

About php servers. Mampp and Mac's php server (which I assume is what valet uses).

2 - What happens if MAMPP is already using port 8888 (or any other) and valet or another server tries to access that? Is the 400 error I get related to that?