I have dwarf hair grass in low light and pool filter sand, it grows but very very slowly and don't expect it to carpet quickly either. I have had it in my 40 gallon since setup, that has been almost a year and its barely spread.
Marsilea Minuta may be a better choice.
Here is what I recommend.
Forget CO2, you don't need it and start up costs begin $200+
Go low to medium light (I would upgrade your lighting) the picture wouldnt load for me, is this a 20 tall or 20 long?
Keep your sand substrate but invest in root tabs and bury them into the sand. You can spread them evenly across the tank or just place them where you plan to have plants that are heavy root feeders.
Then dwarf hair grass or m. minuta in front, some java fern and/ or anubias tied to rocks or wood for mid ground and in the back plant tall cryptocorynes like Cryptocoryne 'balansae', Cryptocoryne spiralis, valsnaria or alternanthera reineckii
With this plan of plants you would only need the root tabs in front and in the back. Anubias and Java fern dont need to be rooted.
All of these plants are pretty easy to grow and don't need alot of light. Check out the second chart in THIS THREAD
to get idea of the lighting you will need.
And if you want to help the plants along, I suggest dry fertilizers and follow EI dosing with Excel. Here is a link TomBarr's EI dosing for less techy folks
It seems complicated but it's really not.
You could also do liquid ferts and excel but liquids are more expensive and won't last as long as the dry.