Welcome to the forum! It's great that you're trying to learn more about the care of your future betta.
To start off with, 2.5 G is just right for one betta! So you're on the right track.
Secondly, I'm pretty sure I didn't see any mention of a heater. Unless you live in a place which is constantly 76+ degrees, you'll need to buy a heater. Bettas are tropical fish and so require a heater to keep their water warm.
I'm not sure how successful cycling a 2.5 gallon will be. Cycling without any seeding generally takes about a month or more, so it could poooossibly be finished by Christmas. If you had live plants or have something to 'seed' your tank with (that is, gravel/filter media/decor from a tank that's already been cycled), your tank will cycle much faster.
OR you could not cycle. Bettas do not necessarily need a filter. If you don't cycle, it just means you have to do more water changes. In my 2.5, I'd do one 50% and one 100% water change weekly. However, you may want to do less than 100% if you add live plants so as not to disturb them (and they will help keep up the water quality anyway).
A varied diet is great! Flakes, pellets, and FD foods (which should only be given as a weekly treat) are fine. I personally don't feed live foods, mainly because it caries the risk of giving your fish parasites and I'm REALLY squeamish.
If you live by Petco, they always seem to carry gorgeous fish...wish I had one here...if you have Big Al's, they occasionally get very nice bettas in. Even Petsmart and other pet stores will get nice boys in once in a while. Personally I go with ones I 'connect' with.