The message you're getting is because to be complete, a community lot has to have all 4 phases complete. The 4 phases are unimproved, maker's space, community garden, and marketplace. Each phase has its own requirements-- the marketplace must have 2 vendor tables, for example. The one I found in the gallery had only the unimproved phase done, I don't know if it was just unfinished, or if that's what happens with a gallery download. Build mode will have the 4 phases as buttons you can cycle through, in the drop down menu you get if you click the lot info bar in the upper left.
Have you voted in the marketplace for your community lot? I don't know if a food stall would be staffed, if the lot was still in unimproved phase.