If you have catfish and loaches, you'll want the tank to have a sandy bottom, with very fine particles. The loaches sift the sand through their gills, and both the loaches and catfish have barbels - projections around their mouth they use to find their food. Their barbels can be damaged in other substrate.
As oldfishlady reminded me, loaches are as social as catfish and should also be kept in a group.
My female VT betta, Baby Blue, is extremely aggressive and killed a catfish I introduced into her tank. She found them to be too active, and chased and flared at them. She is in QT right now and the cats and loach are waiting to move into a 20H once it's cycled.
In a ten gallon, there is room for the catfish and betta... and if your betta is not a manic like mine is, you should be fine. :)
Cories are the absolute best tankmates for betta IMO/E. They can be kept in gravel so long as the gravel is smooth and rounded with no jagged edges. I have mine in a gravel tank and they are doing great. Sand would be even better for cories but it can be a pain to clean. in a 10 gallon with ONE male betta you can get 4-5 of the regular sized cories or 6-8 of the dwarf variety. I only have 3 and its very interesting to watch them interact. Sometimes they'll group together and touch heads. Its very cute. I feed mine 3-4x a week on a diet of sinking shrimp pellets and the occasional algae wafer. They also eat fallen flake food.
I also have a new 10 gallon that i set up about 3 days ago, but mine is cycled. I borrowed a book from my library called "aquarium owner's guide: the complete illustrated guide to the home aquarium" by gina sanford. It gives nice advice, but i hate how she treats fish as objects and decorations and urges you to do a fish in cycle, and says nothing about doing water changes to save the fish. It was written in the 90s though. Anywho, from the book, i thought of getting cory cats, about three. Hatchet fish creep me out. I also considered mosquito fish, dwarf chain loaches [but the book said keep 6 or more], pencilfish, glowlight tetra, bleeding heart tetra [if my betta wont flare and attack it], or a zebra pleco but i dunno... I also considered shrimp. Are chichlids out of the question? The book said they need large tanks, and some are and arent peaceful... I have pebbles on one side, and gravel on the other side of my tank, its polished sorta but kinda jagged gravel. I could use sand in the middle...
Bettas should only be kept with peaceful fish... they don't like overly active tank mates. Chiclids are to aggressive for betta, IMHO.
With a ten gallon you could have cories. I'd go with a dwarf variety. Be careful to check their adult sizes, because some of them get quite large as adults!
Stock your tank for the adult size of your fish (1" of adult fish per gallon of water - and remember, your betta will take up 3"/gallons alone), so you don't overload your tank's bioload as they grow.
Try to get fish that swim at different water levels in the tank (fighting less likely). Bettas are 'top level' fish (they need to get to the surface to breath). Cory cats are 'bottom level' fish. Tetras are 'middle level' fish, and are a good choice if you get a non-nippy kind. Here again, you'll want to go for dwarf size adult fishes, as they are schooling fish and need to be kept in groups of five or more.
A word about plecos - most are big, and some are huge as adults... not a good choice for a 10 gallon.
Finally - a new tank set up takes 4-6 weeks to cycle. The benefical bacteria have to grow and establish themselves in your filteration. Our FAQs here on the forum (fish care sticky at top of page - with a light bulb next to it) have information on tank cycling.
I had a 5 gallon cycled tank before, then moved my betta's filter, plants, and some gravel to the new ten gallon. I mean the itty bitty hatchet fish with the flat bellies called "marbled". Yup, they scare me. I dunno why. They look like they have a protuding mutant-like overgrown chin. Big chins and beards scare me.