Sorry! I answered in the comment. xD

1 is perfect. 2 looks unnatural. When I say "足りる”, I would use like this. ”この本買うのにお金足りるかな・・・？”　（もしかしたら、足りないと思っていた時）" 本買うのにお金が足りないと思ったけど、足りた！”　友達が、自動販売機でジュースを買おうとしているとき、”小銭足りる？””足りるよ！”　など。 It really depends on the situation. The meaning is the same. You just need to get used to it through practice. :) Hope it helps. P.S. I guess in Osaka where I live ,people tend to use 足りる　more than 十分　in dairy conversation. We say both but 十分　sounds a bit polite sometimes. we are not. Lol

So 十分 is more normal in conversation? When would I use 足りる instead of 十分？ Would both of these sentences be natural? 1) 私はこの本を買うのに十分なお金を持っている。 2) 私はこの本を買うのにお金が足りる。

十分 is proper way to say enough than saying 足りています。For example, if you are have coffee and somebody ask you to have more, then when you want to say No, thank you because you had enough. Then we say, もう十分です。ありがとうございます。

Hey I'm not an expert though. I think they are used in the same meaning like "enough".、,also together. 十分足りる。 I'm not sure it's a proper way. But most people talk like that. So I think there is no big difference. For example,十分な食料。食料は足りている。