You have a dilemma! Shrimp don't breed well with high CO2 in the water. And, HC doesn't grow well without high CO2 in the water. (I'm not sure what Downoi requires, other than soft water.) I think most shrimp keepers, who want their shrimp to breed, just do without any plants that have to have good CO2 to grow well.
I think you will have enough light, with 9-10 watt bulbs, to grow anything, but only if you also use good CO2. Take away the CO2, and you will limit your plant choices. Add more light without more CO2 and you will have algae problems.
Just want to let you know so far so good. No yellowing or die offs (yet). 2-4 bps CO2 and lights on 8 hrs per day : )
Would love to see this tank when it gets setup. I drool over those 12g longs...the dimensions are so nice. Gold luck with your HC carpet!
I linked my journal to my signature. Feel free to comment.