Don't! Don't buy any seahorse that most LFS's carry. They're probably tank raised from asia, too small, underfed and diseased. Many people start and give up on seahorses because of the crappy ones that LFS's carry. You want to get captive bred seahorses from a breeder.
Seahorse Source is the favorite in the seahorse community, but you can also check local reef clubs to see if there are any breeders.
I wrote something on exactly that subject here:
http://www.fusedjaw.com/aquariumcare/a-modern-guide-to-buying-seahorses/
As for your equipment, expect seahorses to be at least twice as dirty as other fish you might think of. You want to aim for a flow rate of about 10 to 20 times the overall water volume per hour, but make sure any overflows and in-takes are covered.
Regarding the products you pictured. I don't know what the first one is. The second one, the marine buffer, is just expensive baking soda. You can make the same thing by putting baking soda on a pan in the oven for an hour on 350 degrees. (more info here)
The via aqua is a relatively cheap brand, at least they used to be. I would look for a hagen/fluval, marineland, jager or even an Aqueon isn't bad. The problem with going with a cheap heater is that when something goes wrong, it can wipe out your whole tank; and faster than any other piece of equipment. Pass on the aquatop - I experimented with them and had one that produced stray voltage and wiped out a bunch of fish before I found the cause. UV sterilization isn't necessary but it's nice to have. As for the marineland biowheels, they're alright in terms of a filter, but the wheels always seem to stop spinning. For a HOB filter, my preference is the Hagen Aquaclear:
http://usa.hagen.com/Aquatic/Filtration/Clip-On/A615 though they may have rebranded them as Fluval.
Whatever HOB filter you use, get one that's rated for at least twice the size tank than your's actually is. The rating is basically the minimum for a lightly stocked tank. Seahorses create a lot of waste, so you want something that can really filter. With a 40 gallon, I'd probably go with two aquaclear 70s (
http://amzn.to/11NlTSi). You could do one aquaclear 110, but with two, you can position them so you'll have the optimal flow for your tank.
BTW, I like your method of shopping. I do that all the time now too. If I want to look something up later, just snap a picture. I'm glad I'm not the only one.