The third pic...does it look like this?? As far as powerheads, it depends on the size powerheads you have to deturmine how many you need... Most importantly, you do not want "dead spots" in your tank. So more, smaller, is better than less, larger. As far as where they point, you definately want the surface as agitated as possible, since that is how your tank gets oxygen. But anywhere you place them is fine, there is no "science" to it. The "whirlpool effect" is frowned upon. But mine are dead center on the sides facing the center of the front. Then there are a couple on the back also, all facing front.
YOur powerheads come with a rating. Called a GPH rating That's gallons per hour. Since you have a 90 gallon tank you'd want your GPH to be 20 times that. So totalling the GPH of all your powerheads, it should come to around 1800 GPH. You can however, include the GPH of your filter, protein skimmer and whatever else moves water in this calculation.