Hablaremos luego = We'll talk later
Lo hablaremos luego = We'll talk about it later.
It's a simple thing: In Spanish, 'hablar' can have a direct object (lo) but 'talk' in English can't.
eg: let's talk. talk TO me. talk ABOUT something, etc.
Your second question: 'talk something over' is a different meaning, like discuss the good things (pros) and bad things (cons) and make a decision together. :)