Welcome to the forum: it's a great place.
I only live about three hours from Buffalo -- it's always kind of interesting seeing other people from Upstate on here, though maybe that's just a quirk of mine.
Anyways, as to the tanks, I actually have that 1-gallon tank for my guy whose fins are growing out, except I bought the one with LEDs (for about two bucks more) because I liked the idea of LEDs better than an incandescent, especially for that size tank. Personally, I'm really liking the tank and so is Sharkfin.
If you want to go with a 2.5-gallon, PetSmart also has a 2.5-gallon glass tank with a glass canopy; it's labeled as a Top Fin, but is made my Marineland (a company I really like, personally). I have my other two guys in those and really
like them. I haven't compared them to the 2.5 Aqueon's as far as dimensions, but I feel like they're longer -- could be wrong. My pet care manager, however, has the Aqueon for her Betta and really likes it, as do others on this site, so if you like that one better then go for it.
I actually don't find my small tanks all that difficult to heat properly. For the longest time I was able to get away with a preset 10-watt for my 2.5s until we suddenly got a hot day. I have a 25-watt adjustable Hydor Theo in with Sharkfin that holds his tank pretty steady, which I was glad for because of the size of it (1-gallons can be trickier to heat). My girls have 25-watt adjustable Elites, but the Hydor is smaller and actually has a temperature scale, whereas the Elites seem to work more on a "power" (not the word I want, but it works) basis, if that makes sense.
I ordered two more Hydors for my other boys to replace their 10-watts since weather has been all over the place here and I just don't want to take the chance. Eheim Jager also makes an adjustable 25-watt that, I believe, has a temperature scale as well and I've heard nothing but good about that brand -- I would have ordered at least one of those as well but I wanted one day shipping and what I could find on Amazon didn't have any shipping deals for Amazon Prime. On Amazon though the prices between the two are otherwise very
Be sure to also get a thermometer: the glass ones that you suction cup (or you can float, or some sink and rest on the bottom) are going to be better than the ones that adhere to the outside. They'll read the water temperature itself more accurately. They're only three bucks at PetSmart.
As for the Betta water, I agree: it's basically just pre-conditioned/treated water, so a small bottle of SeaChem Prime is a much
better value. As I tell customers at work: that stuff will last you forever.