Try not to start new threads, get's confusing as people still post in both. You could ask the same questions in here as people that are interested will follow the post to help of for their own interest.
Standard balancer will be fine. Otherwise get a Ross or an ATI if you've got the cash.
Doesn't need to be the same weight as before. Wouldn't hurt to get a balancing/machining company to spin it up to make sure it is balanced.
Replaced your crank keys to be safe, saves it sticking again. Put Molybdenum anti seize on the crank snout too, even further prevents sticking/grabbing.
Underdriven only worthwhile if you're on the track 90% of the time. Gives you lesser P/S and A/C (which many can live with) on the street.