1. If your opponent doesn't declare defenders you automatically win the edge battle, you may however play edge cards if you wish, eitehr to burn bad cards in your hand quicker, or to use target of opportunity for example.
2. You only count the force icons on cards you play in the edge battle, not the units engaged, the exception to this is if any of your units in the engagement have Edge [x] on them, in that case you add that number to your side of the edge battle, cards with this so far are limited to Mon Mothma, Edge , and Speeder units when you have the objective Hoth Operations out, with more Hoth objectives than your opponent.
Hope this helps!