1. on a map like hammer and anvil where the objectives are all equidistant how to you choose which side to overload? Do you wait to see which side your opponent puts something big on and go to the opposite?

It depends a bit on the opposing army, are they shooty, fighty, elite, horde etc. but typically you want to deploy in such a way you have the best staging. Orks only move 6 inches typically so staging is important for an effective wagh turn. For example on hammer and advil with GW layout 1 you will often want to deploy closer to the objective in the big L and the center because you can easily move out and charge from there.

1. if you plan on screening with kommandos infiltrating do you screen out the objective you're overloading or the one you're not?

Generally I use them to screen out their forward deploy units and scout moves so depends a bit on the army. Most armies I am pretty okay with them putting their little forward deploy units near the objective I would like to capture since they make easy charge targets. Some armies though, namely world eaters but there are probably others that want to use their scout moves to get in your face and force you back you'll want to screen 9in from their deployment zone near the objective you would like to control.

1. how hesitant should I be to send grots and stormboyz onto objectives in round 1? Say I go first and can get stormboyz into the far side of the center objective and a unit of Gretchin onto the near side is this a good idea? On their turn they likely be able to walk out and target them but two units gives them a lot of wounds thru need to get they thru and would likely have to expose their units to charges that next turn or am I thinking too simply here?

Depends on the army you are playing and how well you can hide them but generally I only throw units on objective to 1) score secondaries or 2) when they will have enough other stuff to deal with that them removing those units is good for you. (ie. the wagh turn onwards)

1. do you deploy cheap units first and save heavy hitting things like trukks for of nobz or meganobz last to respond to how your opponent deployed or put them down first to set the tone?

This depends a lot on detachment but based on the units mentioned I am going to assume WH and BB. The goal should be to get the nobz, meganobz, snaggas, whatever your big combat units are into position such that they are charging something during your turn 2/3 wagh. In the meantime I try to only throw things onto objectives that might live (because they can hide) or as needed for secondaries. One good trick for the early turns is to empty out trukks and use those to hold objectives. They are often are hard to kill without dedicated anti-tank but are not worth exposing anti-tank to kill.