Yes, those would be the basic steps, though a Prom upgrade is usually not required unless too old.
Disconnect the Pulse cellular/broadband communication devices before installation of the SEM.
I cannot vouch for any specific third party seller, though Vista is a popular panel and a number of vendors online offer parts.
Activation of your service on our website is a step by step process. Your new Alarm.com account is automatically created as part of activation.
You will need to know the current installer code of the system.