I am clueless when it comes to electronics so bear with me. I'm comparing alarms and the one w/the 5-channel has a remote start which I don't need. What advantages does a 5-Channel security system have over a 3-channel? TIA.

 

I think you are referring the the amount of outputs the alarm has.
A 3-channel one would have outputs for
1. remote start
2. trunk release
3. window roll-up

 

Below is the description of a viper alarm. I thought the 3 auxiliary outputs were the ones used for features like remote window control, trunk release, etc...

Viper 791XV 2-Way Security and Remote Start System with Responder Technology 5 channel security/remote start* system with 3 auxiliary outputs for additional remote control conveniences.*

 

If refers to remote controller. Different outputs per channel on your remote. Different button combinations on your remote access different options.