Camshaft does not give your engine compression. that has to do with the pistons (dome, flat top or dished), block (deck height), and heads (combustion chamber size).
they are saying the minimum requirement for that specific camshaft to work correctly, a camshaft will effect the compression ratio because of overlap letting some of it out. the cam that requires 10-1 will let too much of the pressure out on a 9-1 engine and you will loose power.
As for EFI there are several out there, I personally haven't ran any yet but have looked into it. The Holley system seems to be over rated according to reviews.
FiTech seems to be a pretty decent alternative. but if at all possible multi port is the way to go.