If you find the right amount of light, you can grow a decent variety of plants without co2 or excel. Check out my 26g bowfront in my sig for plant ideas.
In my opinion, definitely do a dirt substrate with a sand cap. If you want a nice cheap black sand check out black diamond blasting sand. Looks great! My friend has it in his 75. As for fish, most community fish won't eat plants...
Great tank!! Thats the exact road I want to go down. I'll have to shop around for a big log like that. No local shop around beside Petco and they dont have much selection.