Welcome to the site and betta fish! Starting out with a 10 gal is a great size.
1. The best heater for that tank is a 50w submersible adjustable heater. I love the Fluval 50w heater, but I think the Aqueon Pro 50w fully submersible would be best. You can lay it on its side at the bottom of the tank to provide more even heating.
The best light depends on whether or not you want live plants. If you do, I would recommend getting a single fluorescent T8 tube hood. Replace the bulb it comes with to a 6500k plant bulb if you want live plants.
2. Sponge filters are best for bettas. They are much gentler on the long fins than the normal filters that are sold for10 gallon aquariums. They will also be cheaper in the long run as you don't have to buy replacement cartridges for them.
3. There are a lot of good plants for beginners. Anubias, java fern, anarcharis, hornwort, duckweed, water sprite, and many others. With the right light and some fertilizers most plants will be in your reach, well aside from the plants that get too large for your tank.
4. If you stuff the 10 gal with plants, he won't look that lonely. Betta are naturally solitary creatures, so he will be just fine in there by himself. But if you do want to add some buddies for him, harlequin rasbora
, ember tetra
, and glowlight tetra
are good choices. All of these fish should be in groups of more than 6 as they are schooling fish. There will be some infighting in the group, and to prevent this from extending to the betta, have more than 6 of that species of fish. Another option is small catfish like corydoras. Bronze cories
are a great fish. Almost any of the Corydoras
species would do.
5. To make sure you do this right, you will want to cycle your tank before you add your fish. Live plants will help you cycle with a fish-in cycle, but they won't eliminate the danger. You can read about cycling techniques here: A Beginner's Guide to the Freshwater Aquarium Cycle