the reason why i wanted to do encryption first is to give the compression more data to work with to find similarities with.

Ain't gonna happen. What makes strong encryption strong is the lack of similarities between different parts of the data. Ideal encryption would produce output completely indistinguishable from random noise. Compression algorithms look for patterns in the data they're compressing. So do codebreakers.

This brings up an interesting question: could one use a compression utility to test the strength of various ciphers? I'd guess that most compression algorithms would look for very naive (cryptographically speaking) patterns, so the "compression test" would only weed out particularly simple ciphers, but I don't have any data or citations to back it up.