powerhead advice...

Powerhead selection and placement tends to consist of a lot of trial and error. Each tank has its own set of factors that make it difficult to give really specific recommendations.

It's really going to depend on the types of coral you are looking to keep. If you're thinking mostly Acropora species, you'll want far more flow than if you want more fleshy corals like open brain corals, hammer, frogspawn, and so forth. The density of your rock piles will effect the flow in the tank (tightly stacked rock = very little flow passing through) in addition to location of the rockwork.

4 x Koralia #2s should give you better flow options than 2 x Koralia #3s, but I can think of situations in a tank of that size where I would consider neither adequate.

I have 2 Koralia #4s, 1 Koralia #2, and a Maxi-Jet 900 in our 90g and I find myself frequently thinking that this is barely adequate flow, even though there are corals in it like hammer, frogspawn, bubble, blastos, acans, duncans, and Scolymia. On the other hand, I have a 250g running mostly as a coral holding tank (minimal rock work, no real vertical piles) that has two Vortech MP40s running at about 80% in constant mode, and they provide all the flow I need for Montiporas and Acroporas to get decent flow without blasting the hammer, frogspawn, and torch coral colonies in the tank.