Nishdu

My new house was pre-wired for a hard wired alarm which I planned to fit myself. The guy who run the cabling did a good job except he did not wire for contacts on the doors. There is no chance to wire them now as I cannot run cables thrugh the dry wall panels. My solution I think is something like a Homelink 55 I will have 6 PIR, three door contacts, and two RKP's as I have a point upstairs for night setting the system. Can I add a second 9943 RKP to the Homelink 55 ? The Homelink 55 has 6 wired zones which would cover the PIR's. I hope I could use wireless contacts for the rest. Prox tags would also be a nice addition. Grateful for any advice.