Dear Agas,
Hope my experience in Cambodia would help your wetland problem.
We applied vertical flow wetland for septic tank effluent for school with a loading rate of 20 to 40 gCOD/m2/d.
If you want to treat it with horizontal flow, then you need to apply with lower loading rates than vertical flow.
The drain in vertical flow must be free flow to allow easier oxygen penetration through drain and ventilation tubes.
The O & M aspects; You can grow reeds but also corn. The reed may help som oxygen supply, but it is difficult to find how to use after harvest.
The corn can be a feed for animals. There would be some residues on the sand surface, and you can remove them by hands after every harvest.
Hope this would help you how to design the V-flow CW with O&M.

Euiso Choi
Professor Emeritus
Korea University
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We are preparing to construct a system to treat septic tank effluent from about 30 septic tanks using two horizontal flow reed beds. 
We are located in Botswana, with a generally hot, dry climate. 
I would be glad to hear of experiences with similar projects, including design recommendations, operation and maintenance requirements and lessons learned. 
Many thanks,
Agas