Good morning, I'm Tech Michael I will be happy to help you with this.
Yes first of all you will need a splitter for the antenna if you wish to use the existing antenna. But, I would purchase a separate antenna for your new system, it will eliminate any possibilities of cross talk that can happen if you have it wired that way even with a good splitter.
This is easy to install and I will help you every step of the way if you get stuck. ALso I will offer you a phone support special service. If you accept that we can talk on the phone anytime while you are installing this. Or if you have any additional questions for me. If you don't accept thats fine too we can then continue like this here.
As for the old plotter yes that should work fine ( be compatible) as long as that one is in good operating order;-)
Like I said, i will help you anyway I can, just ask.
Please rate my service to you kindly at this time or accept the phone offer, that will keep us locked in no additional cost to rate. After you rate, you can reach me anytime by replying to this message again no additional costs associated with this help request.
Thank you and have a wonderful day!