The thing with bettas is that they're very curious, intelligent fish. While they can live in little bowls and be perfectly healthy physically, it's really cruel. It's sort of like how a person can live in a closet so long as they have food, air, and water. Would you want to?

I have a two gallon hex that sits on my desk, and since it's so tall, it doesn't take up any room, but it's big enough to have rocks and plants in, and my betta can swim around. It's also large enough for a filter and heater, which no fish should really be without (unless they're cold water, of course). Filters also make cleaning much easier by keeping all that filth off the bottom.

As for putting your betta in another tank sometimes, I don't think that's a good idea. Changes like that put stress on fish, and you shouldn't move them around if you don't have to. I would think that it would also make it even more depressed about being in a little bowl again. (Not sure about the emotions of a fish, but I've learned from my Fred that they have a lot more going on in their heads than people give them credit for.)

What your betta will eat all depends on the particular betta. I have pellets, freeze dried whole bloodworms, flakes, and freeze dried brine shrimp. My last betta would touch nothing but bloodworms, and my current one wouldn't eat anything at all until I put him in a heated 10 gallon. Now he eats flakes, shrimp, bloodworms, and he even has a few pecks at algae wafers now and again. I hear that most bettas love the Hikari pellets. Mine are a different brand, and larger. I guess they prefer small pellets?

A betta should do fine with a pH of 7.4. 8 is their limit, so I wouldn't go over 7.5. There is a way to lower it, but I've heard that these products aren't always a good idea because your pH can go back up after using them, and having a pH that fluctuates is a lot more damaging to fish than a constant pH is, even if it is a little off. They can usually adapt to something that's constant. I wouldn't toy with it unless it's way outside the range of your other fish's needs.

How big is your tank, and what fish and other animals are in it?

And yes, you can use old aquarium water in a new tank. Using plants, gravel, and filter media from a cycled tank will also speed up a new tank's cycling process.

My opinion on minimum betta care:

1)A tank of at least 2 gallons with full access to the surface

2) Heater 25W or lower. Lower is better, but they usually don't have auto on/off and you can't set them for a specific temp.

3)Decorations, plants, and hiding areas. Gravel is not necassary and can be a burden if you don't have a filter and syphon. They don't need an air pump.

4)Filter is strongly recomended. Without a filter in a 2 gallon tank, you'd have to do 100% water changes at least twice a week. With a fully cycled filter, you only have to change part of the water every one to two weeks. Its much less stress on the betta. Pick the smallest and least disruptive filter you can find. A good one is the Red Sea Deco Art Nano. Do not change the filter pads. You can fully cycle the filter by running it on your other aquarium for 2-3 weeks.

5) Specialized betta food. Bettas have different nutritional needs than most other tropicals and benefit from a food made specifically for them. I feed Hikari Betta Bio-gold baby pellets. You can also supplement with pretty much any live, frozen or freeze dried food, just not tubifex.

6) Airline tubing or small syphon. This is necassary to suck up gunk on in the tank, especially if you have gravel.

7) Water conditioner

Hope that helps :) Kitty gave excellent advise, especially about not lowering pH.

I almost forgot. Whatever enclosure you decide on, make sure it has a lid. Make one if you have to! Bettas are natural jumpers and so many have leapt to their deaths...or near deaths if they are lucky and found in time.