I watched the miniseries then the show, and there was some additional stuff I watched also but I don't remember exactly when. There was a spinoff called Caprica, it was good but never got a second season.

Here is a watch order that includes a couple movies and webseries, but it puts Caprica at the beginning. It is a prequel but I think it would be better watching it after everything else like it was released.

Edit: if I remember correctly Caprica either has some serious spoilers or there are some things you wouldn't understand if you hadn't seen the main show, I don't want to say anything more but I don't know why they recommend it first.