Male bettas especially appreciate very slow water movement.
You earned it... Lovely fish. GREAT coloring. He doesn't look like a marble to me, so I doubt he'll change to all red... but then again, what I know about bettas is extremely limited, so its not outside the realm of possibility.
I am extremely happy that you were willing to wait as long as you did. Your substrate looks plenty deep for plants. The nice thing about your substrate choice with plants is that the roots should move into it easily, and fishie poo will also move into it and become nice fertilizer for your plants. You'll get a very nice little ecosystem going there. Just feed the betta and change the water regularly. I don't foresee a need for ferts or gravel vaccing. Just watch out that you don't overfeed. Limit the bloodworms, and stick to primarily a diet of betta pellets... not too many.