Rice paddies aren't exactly their true native habitat. They live in them the same as mice live in the walls of houses. Not to mention the fact that betta splendens as you would find in a store is so far removed from the wild type that no true biotope can be made for them unless you find one very close in color and finnage to the original. Not impossible, but difficult.
A betta splendens as per pet store with its bright colors and flowing fins would be a big blinking "eat me!" beacon to predators in their original biotope. This would be peat swamps, bogs, very slow streams and shallow pools, and rarely, large puddles leftover from floods.
Anyway, if you are into the idea the best information I have for plants they might encounter in their native habitats would be blyxa spp, hygrophila corymbosa, pogostemon helferi, cyperus helferi and by introduction there could be java fern and java moss.
Little current if any. Remember they are a labyrinth fish and as such can live in almost completely stagnant conditions. (Not saying you should subject them to that though!) Subdued lighting either from low wattage or from a plant canopy. (Cyperus helferi is great for this application.) Substrate would vary depending upon the location - but much of their geographical area has iron rich substrates and laterite deposits. Lots of mud and sediment as well. Plenty of organic matter especially in the peat swamps. But I wouldn't recommend the peat in your substrate as it can lead to an overabundance of organic matter. Maybe look to a reddish sand or Flourite or a mixture of both? Use peat filtration however. If you have ever seen the colors of a betta in a black water tank you would be sold on it as I am.
Hope this helps.