1 gallon is enough, but I personally think 2.5 is a minumum. That is MY minimum at least. They seem happier with a little room to move.
Tank mates are unneccesary... Not just unnecessary, but unreccomended. Bettas are naturally over-territorial, and get very aggressive to other fish near them. They do not get llonely (unless you have one of those freaky ones who's depressed without tank mates like my lte Lemon Soda, but that is VERY rare). If you really choose to have a tank mate, an african dwarf frog is acceptible, as most fo them won't notice eachother, since bettas are top dwellers and frogs are bottom. But personally, i like to keep them alone.
For a kitchen, I think a 2.5 or a 5 gallon is best. When I have bettas in rooms beesides my bnedroom (which i DON'T, but I think about it a lot) I try harder to keep the tank nice-looking, since a lot of other people see it. So you may want to consider a 2.5 or 5 gallon hex tank. These are not best for the bettas, but are still acceptible, and a lot of people think they look nicer. But if you just want simplicity, a 2.5 or 5 gallon rectanglular tank is best. A 10 is also great, but I doubt most people have couterspace for a 10 gallon aquarium!
Lastly, just a last little note to think about - If your betta is in the kitchen, and will therefor be frequently seen by others, you might want to consider getting a 'fancier' betta, as opposed to the common VIel Tail you find in petshops. Though there is no difference in temperment in most cases and both make excellent pets, I think for something that is being a decoration as well as a pet (never JUST a decoration...) that little extra kick makes a great conversation peice, and if it is your first betta, it is really great to have something unique. You are more likely to really love them when you're new, when you have something nobody else has. (though when you realize all bettas are equal, you reallly love them all the same, even when they are just vieltails!)
Oh god. I did it again. Wrote a 2 page reply to a 2 sentance post. Someone please put a limit on my posting size >_>
If you decide to invest in a betta, make sure you have the time to take good care of it, really enjoy it, and love having him
*wonders if anyone is still awake after all that...*