>What IRC clients are popular amongst Trisquel users?
I wouldn't know, I imagine Pidgin is the most widely used.
Irssi is my favorite -> https://irssi.org/
>Also, what is a good way to secure the connection? Using SSL?
Sure. Here some basic info to get you going in case you decide to go for it
> Is it good practice to securely connect to IRC?
It is. Indeed securing any connection is always a good practice. Encryption