Sure a single betta in that is fine, he'l have lots of room, but he'l also probably want some plants and ornaments to take up dead space - you wouldn't want to live in an open warehouse would you? He'll love all that space so long as there are things to swim around and/or under. They prefer to go to what they feel is a safe spot when the lights go out.
In a tank like that you should go ahead and get a filter, and do 50% water changes every week. If you have live plants (which I recommend) and a fully cycled tank then you can probably extend that to every 2 weeks. You don't want to wait for ammonia to approach any noticeable problem zones, you change the water on a regular basis.
I honestly don't do 100% water changes, good bacteria can live in the substrate and also for getting plants - they'l need it. If you get any tank mates (like catfish) they'l also prefer it (something smooth or not too sharp). Not to mention gravel makes a tank look great. Water changes are not hard, I use a bucket and siphon hose and it takes me less than 5 minutes (I use the water hose outside to refill the bucket). I have a 16 gallon tank and I've actually only had to change the water every month (it has lots of live plants).
10 gallons is not a large tank, it should be easy to care for though, the larger the easier the maintenance can be actually. Water quality seems to be much easier to keep when there is more of it.
If you want to have a lot of awesome tank mates, maybe pick a female betta? They seem to get along (but consider they all have different personalities) better with other fish than males do. A tank that size deserves to have more than 1 fish - but that's your option.