sump help

[sea gnome]

Ok, was going to get stuff for sump. Ie: pumps and phoned around, seems like people were trying to sell me little giants and not mag 12's. Thoughts?????? Also what size pvc piping is everyone using. Seastar has agreed to drill tank and will provide 1.5" bulkhead fitting for $35.
One shop said I would need 2 holes for a 90G. Thoughts???? Do I need a pump size of mag 12 to power diy skimmer or could I gett away with something smaller. That's all for now but I know there'll be more later!!!