Advice requested: about to liberate first region, it has Strength of 1 and high vigilance, should I wait until more ADVENT legions move in?

Playing Long War 2 on veteran difficulty (that's 2/4). I have recently researched laser weapons and have access to Assault HQ mission. Should I go for it or wait until more troops are transferred so I can kill those ADVENT legions?

The haven already has 14 rebels.