With anacharis or hornwort, you would be fine with that substrate. Those plants will only sink when weighted (many people leave them floating, i like mine weighted) and their roots suck nutrients out of the water. You may have problems with some plants that have very agressive root systems (like my onion plant) though. Id stick with anacharis, hornwort, or maybe a java moss. Those are low light plants, very easy to grow (you'll have to prune them periodically) and will build up your confidance.
I havent heard of bettas getting tangled in plants, but I guess it could happen. Keep an eye on them for awile, but they should be ok.
I havent heard of bettas getting tangled in plants, but I guess it could happen. Keep an eye on them for awile, but they should be ok.