I've seen those tanks, they are actually really thin. The heater you show I have 5 of (i have 9 bettas). I like that heater alot, it works great!
If you're looking for a tank from WalMart in particular try these:
I own this one, I would get rid of the under gravel filter and replace it with the one I show at the bottom:
I have this one too, I love this little tank, it's just like the one above but shorter, it's also a good idea to replace the filter
They are great because your Betta cannot get caught in them like most filters.
You don't need any type of aeration since Bettas get most of their air from the surface.
Here are some things you'll want to look for for him:
-Silk plants. If you're new to fish keeping you don't want to dive into live plants just yet! Plastic plants can easily rip your Bettas fins apart. I suggest looking at PetCo or PetSmart for their silk plants. They are easy on his fins so he wont get tore up. Bettas love lots of plants and they love to lay in them and explore. You're going to want to have lots of hiding places for him so he doesn't get bored or stressed out.
-API Stress Coat+ .. This stuff has water conditioner in it already, so you can use it along side or in place of your regular water conditioner. It will help your guy not get so stressed out in his new home. You're going to want to use it every time you change his water. They don't sell it at WalMart you'll have to get it at PetCo or PetSmart, it may be at your LFS (local fish store).
-Betta Candy! Froze or freezedried, it's up to you! Frozen is much more nutritious then freezedried, but the freezedried stuff isn't as messy. Bloodworms, Glassworms, Brine Shrimp and Daphnia are all yummy treats for your guy. You can feed them along side or in place of his normal food. You only want to feed them to him 1 - 3 times a week though. They are just "candy" for him.
Foodwise you're going to want to look for these brands (they are my favorite):
New Life Spectrum (NLS)
for Small Fish (my favorite:
Omega One Betta pellets and flakes:
Aqueon Betta Pellets:
(can't find the link, they sell it at PetCo)
No matter what the label says, all Betta food will help increase and brighten the colours of your Betta fish.
Flakes typically cloud the water up and they are a bit more difficult to tell how much you are feeding your fish. I suggest pellets over flakes, but if your fish doesn't like his pellets even if you try soaking them then you might have to use flakes. I have a fish who will not eat pellets no matter how hard I try, so I have to feed him flakes.
I hope some of this stuff helps you out. If you are interested in takes that are not from WalMart I can show you acouple others that I really love as well (that aren't round lol). I have 9 Bettas, most of them are in 2.5 gallons or 3 gallons, the largest tank I have is a 5.