[Question] Setting up Docker on an already functionning server?

Hi! I'm still learning a lot. I have a raspberry pie (on raspian) with pi-hole, pivpn and outbound as a dns resolver. The next step will be for me to set up nextcloud. But I'm reading a lot on docker and containers these days and want to deploy docker now. Should I start again from the begining setting up docker and after pi-hole, pivpn and everything or could I keep everything the way it is now and then installing docker? The latter would be the best for me, but I don't know what to look for when installing docker after pivpn, pie hole etc. Thanks you a lot for the help

EDIT: Thanks everyone for your response and help!! You gave me the confidence to just try it and learn by doing it