Adding cb to 2013 Mack pinnacle

I’m looking to get a ch added to my 2013 pinnacle. In the overhead bin I have the power/ antenna connections. The drivers side mirror has an antenna ( I assume am/fm) pass side has a stud but not antenna, so I am assuming it’s all setup to throw a cb in. I’ve never installed one, any tips? What size antenna should I get? 4ft fiberglass whip?
Seems like the radio install is pretty basic, it’s just tuning it that’ll take a bit of patience.