the spike suppressors tend to be fitted in the panel and aren't expensive so it would be up to you. I always carry a few just in case but if your not fitting many alarms then the chances of you needing them are slim. as long as you keep your mains cable and alarm cable segregated then there shouldn't be any need to use screened cable. you can cross mains cables at 90 degrees without any worry at all. if the alarm cables have to run with mains at times just keep it to a minimum.
I agree with james.
if someone can take control of your ARC, then they could gain access to any or all of the sites you monitor, with little risk of getting caught.