What is the timing on the use of free actions (such as force push)?

Can I: Move - Move - Force Push - and THEN attack because I have relentless/charge?

Which page has the relevant rules on using free actions and their timing?

ALSO...

Can I force push an enemy unit, and place one of the models in the unit into melee with me, even though the unit leader couldn't move far enough to touch my base?

Cheers

All free actions triggered by other actions need to be done immediately. You cannot pause your charge for force push.

It's on page 12 under abilities and timing of "after" effects.

Only unit leaders can start a melee. So no, you can't "cohere" into melee, not even with force push.