Would you be allowed to add a blank with Finn then trigger Han (original trilogy)?

You sure would be. You choose the order to apply your effects. The big things to remember are:

1. You can't reroll the same die twice.

2. You can only do any given thing once per opportunity.

3. You can only spend one token for it's standard effect once per attack.

Yes.

It's too expensive IMO but add a die with fun and reroll with Han and now he's a four die attack, PWT, 5 if range 1. Gunner gives you two tries st the big hit if the first flops.

*Finn