some systems will record both streams for remote playback. I use this then can find the incident quickly, then view the hq stream one the time is found etc
bear in mind a dialled isn't signalling. And as you have found out, the path isn't popped and you don't know if its working. I personally hate diallers. Better to use even a digi or sim based device that is polled
it depends on risk, building type etc. Id say as a minimum all external doors and double detection ground floor areas. Then trap protection corridors etc
fss means nothing. How many times have you had Signal but can't make a call. If the signal is important use something that polls and ensures the path is actually there.