The fact that you are here asking about filtration, surely means that you understand that you need your filtration to be adequate for the health and success of your aquarium.
You will be placing more strain on your future system by including the under gravel filter (UGF) than if you didn't have it. Surely you'll want the waste from the many fish(es) you'll buy to be removed by whatever filter and media you choose, your skimmer and the substrate vacuuming which you'll do when you do a water change. You don't want to allow the UGF to pull the waste into the gravel where it will sit and rot and pollute your tank. You'll be fighting an uphill battle all the way. I think you should remove the UGF but keep the powerhead for water movement in the tank.
I know you didn't ask about the UGF but isn't that the beauty of free speach in a civil society? *celebrate
I have no experience regarding the filters you have listed (I use a Fluval 400) and so can't help you there. I can tell you that Eheim is a decent brand.
Fianlly, a recommendation that I'm sure will be repeated to you a few times is that you should go and buy, read and digest the book "The New Marine Aquarium" by Mike Palleta. If you want to take that a step further then read "The Conscientious Marine Aquarist" by Robert Fenner also.