A couple of things you could do:

because you have FILEPATH in multiple places, try this at the top, so you only need to set it once. Then call it with $FILEZILLA_FILEPATH.

alias -l FILEZILLA_FILEPATH return FILEPATH

your server and channel could be set this way (called a constant) as well, so you aren't using extraneous variables. As far as why you have a specific server set, it looks to be so it automatically starts only on the IRC server you want (incase you connect to multiple).

I also suggest commenting the hell out of your code. Every couple of lines or every scope change, so you know what you're doing there if you ever have to come back to it.