Hi Jon! Welcome to Fishlore! It sounds like you're going to be a very successful aquarist and get maximum enjoyment out of the hobby, whether you just have one betta (very satisfying in itself) or eventually wind up with a community tank.
You've already done quite a bit of research and ask very good questions. I think a lot of people impulsively decide they want an aquarium, rush out and buy it with having no clue about the
nitrogen cycle, overstocking, what kind of equipment they really need, etc. You're way ahead of the game.
1 - If you decide to go with a ten-gallon, that would allow a bit more flexibility. For example, you could get three pygmy Cory catfish to go with your betta. (Most, but not all, bettas will accept them as tankmates, not that they
need fishy "friends." You'd want to introduce the Corys to the tank before the betta if you decide to go this route.)
Marineland also makes a six-gallon Eclipse, so you might add this to your list of options to check. The filters that come with the Eclipse tanks are excellent. The filtration system includes a Bio-Wheel. Probably some filtration systems with the other tanks are as good or nearly as good, but that would depend on the tank.
I'd steer clear of the hex tank for reasons already mentioned, plus several owners have reported problems with reflections, therefore causing their bettas to flare excessively.
2 - I used Bio-Spira and got unexpected results, although most people reported spectacular results with it. I suspect the stuff hadn't been handled properly in transit to the local store where I bought it, as it had to be refrigerated. The Tetra SafeStart does not have to be refrigerated, and I've read equally favorable reviews on it although it's a relatively new product. If you want to try "instant cycling" with SafeStart, you'd probably need to order it online but shipping would not be nearly as cost-prohibitive as Bio-Spira. The status of the two is unclear to me, but I know Tetra's parent company bought out Marineland, makers of Bio-Spira. I think they're phasing out Bio-Spira if they have not already done so. I couldn't find SafeStart about a month ago anywhere, though, but did find Bio-Spira.
In addition to the Bio-Spira experience, I used the fishless cycling with ammonia, following the directions exactly from the link Lucy provided. It works!
However, by far my best experience in cycling a tank was to seed it with used filter media from the tank of a friend who I met here on Fishlore, Martinismommy (Karen). It was for all practical purposes just as fast as the "instant cycle" products and I trusted it much more. I added her used filter media and the betta at the same time, monitored the parameters, and it was amazing how quickly it worked, plus there were no danger-level spikes in ammonia or nitrite. If you know someone with a tank you trust, that's the way to go. By "tank you trust," I mean a long-established tank with healthy fish and no new un-quarantined introductions.
3) Like most people here, I highly recommend the API master test kit. Don't get fooled by those easier-to-use and less expensive strips. They're notoriously inaccurate. Luna was right to suggest shaking the #2 nitrate test bottle vigorously. Their instructions say to shake that bottle 30 seconds, but really, you have to shake it
vigourously for 1-1/2 to 2 minutes, including knocking it on a countertop a few times during that time. That's my only complaint about the test kit, and I think I lost two adorable Corys because of high nitrates that weren't showing up simply because I followed their directions exactly and didn't know better. Otherwise, the directions are very good and they provide these neat little "cheat cards" for each test.
I'm excited for you getting your first fish, too!
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