That's most of the questions, thank you. You haven't said whether the psu can be the other way up or not however. I can't be bothered to ask google.
Two fans as front intake. The one with the hard drives behind wont be achieving much beyond keeping them cold, but this is fine. Top two as intake. H50 as exhaust. Graphics card also acts as rear exhaust. Turn the psu the other way up if possibly you can, despite there being a pretty grill below it.
You need balanced airflow, not savagely positive pressure. This is why turning the psu over will help. Second, you do not want hot air coming out of the graphics card then being drawn straight into the H50. Third, top intakes will keep the air over the cpu socket pretty close to ambient, allowing the H50 access to cool air and keeping the ram from overheating. A potential issue is the motherboard chipset; if you have options for moving the graphics card you may want to consider moving it down and leaving the psu with the intake downwards.