I am thinking to install remote starter and after some search I didn't get enough info and got confused

. One of the old post says it is bad to leave the car on idle because it is going to take longer time for warm up. Is that right?
My second concern is what would happen if I start the car while the alarm is on? Do I have to unlock then start it? Because I was thinking to install just remote starter not w/after market alarm.
I know our cars are manual trans and if I forget at gear I am gonna get the beast down the street and so on

. That has been thought.
Thanks for any info

.