[HELP] Need Hardware guidance before I begin

Hi, we have a Norstar M8x24 w/ DR5 KSU, 4 phone lines to our telco, and about 12 M7310 stations. Currently we don’t have voicemail but I’m exploring how to do this with Asterisk. I need to understand what hardware I need to connect an Asterisk server into the KSU and the ballpark costs for the equipment, or whether the KSU should be removed altogether. I can’t find a simple explanation in the documentation.

Thanks all.