I recommend replacing your old panel with a new one instead of a DIY box of relays. By installing a new system you get a UL listed panel, which is important for your insurance discount. It will have all the things you would have to DIY already built in, like battery charger and central station communicator. Most are hybrid systems which can be wired and/or wireless. A basic panel with a keypad, battery, and transformer can be gotten at a reasonable price. It will have options for complete system arming (away) or just perimeter arming when you are home. You can add other accessories later, like motion detectors, etc.