Going from top to bottom of the links you posted:
THe first link has that Koralia that's too powerful, then some food that I'm sure you weren't looking at, and then a maxi-jet 400. The maxi-jet isn't a bad powerhead, but you would need to do some foam around the intake because the horses tend to get trapped against those powerheads easier than with Koralia 'heads.
The second link is to a big ol' Mag 18 return pump. Don't worry about it - you don't need that.
The third link is for a protein skimmer I've never heard of before, so I can't speak much to its usefulness. I noticed however that it looks like an limewood-driven airstone style protein skimmer. If you can, pass on the airstone style skimmers. They don't "chop" the bubbles fine enough to get a really good skim. I used one by Oceanics for a while and.......meh. Also you'll notice the price isn't really a great deal.
The 4th link is for a seaclone skimmer. Not bad. Not great, but not bad. You can do some reaserch on line (and even on these boards) for people who have seaclone skimmers. Of all the things you're going to put in your tank though, the skimmer and the chiller are the things you shouldn't skimp on now.
OK, the last two links are for a fluval canister and a classic eheim canister. I'll tell you flat out that I don't have ANY experience with canister filters - I have used HOB (Hang On Back) style filters such as the Emperor 400 and the Marineland 280 that you have, and I currently use overflow style sump and refugium filtration for my tanks. The TOM Aquatics Rapids filter I have on my seahorse tank now is the closest I've ever come to a canister filter; it's sort of a hybrid filter that has canister and trickle filter qualities together. I don't think you REALLY need this size filter, but I highly recommend you do some research on this before you make your decision. And I'll remind you - I'll be glad to give you my Emperor 400 if you'll cover shipping.