You never do a 100% water change in a cycled tank. It's only a partial in a cycled tank; you don't want to lose all the bacteria that is clinging to the surfaces within the tank. In my 5G/cycled/planted tank, I do about 30% every 5 days. I don't know if I could go longer between changes (like once a week). This is what is working for me and my water parameters are steady.
It's a good idea to have a liquid test kit for checking your water, especially if you plan to cycle. The liquid test kits are more accurate than strips; the API master kit is a favoured one.
As well, consider the food. Pellets tend to float and be cleaner than flakes. Flakes will sink and are messier as far as keeping the tank clean.
For plants, I recommend getting anachris and letting it float. Petsmart does not usually have it. Petco does but make sure that it looks health, i.e. it should not look brown. Petco also has java ferns. You tie them onto a log. You could also get a small sword plant or a wendtii plant since you will have a substrate. Moneywort is good. It's roots are very small, so it tends to float. Either tie it to something with some thread or keep the lead weight on if it comes with one.
Buy either Prime or Amquel to condition the water.
You need a test tube type aquarium test kit so that you know when you need to change your water. I do a partial water change once the amonia goes above .25 ppm. I noticed that Petsmart sells a test kit for just amonia that is less that the complete test kit. I'm a couple of weeks into starting a new 5 gallon. Initially, I was changing water (2 gallons) every other day. Now I'm changing about every third day.
How's your tank stocked? Feel free to PM me.
Live plants, driftwood and one betta only in each tank. I have never been a big fan of putting male bettas with any other fish. I have found when I have tried it that the bettas are either bullies or get bullied.