Is "Module::Crypt" good enough to encrypt a perl script?

What is your definition of "good enough"? Note that there are no 100% perfect solutions - simply put, in order to run your code the computer is going to have to see it at some point. Also, you've read the documentation of Module::Crypt, right? In particular the Abstract? "... please keep in mind that nothing will keep a determined person from cracking any defense. We can only hope that with Module::Crypt it will take a seasoned Perl wizard to do this, not ordinary Joe Wannabe Cracker." See also How can I hide the source for my Perl program?

Would the script's execution slow down after it is encrypted?

Loading the script might be a little slower, but once it's compiled I think it should run at the same speed. But the only way to know for sure is to measure.

running into errors, please see below the cpan install log.

The errors say "Can't exec "gcc": No such file or directory", so it sounds like you don't have the GNU C Compiler installed. It looks like you're on some *NIX system, so you should be able to look into your package manager's directory for the package that contains "gcc". For example, on Debian-based systems like Ubuntu, sudo apt-get install build-essential.