Haven't personally had them but I've seen them at 8-9 inches and reports, but not photos, of 11 inches. TUIC currently has some at 9 inches.
I haven't seen much of on care out there, maybe because it's similar to most true geos? So unless someone can speak from experience, I'd expect similar care and tankmates to other medium to large geos-- sandy bottom, good sized tank for adults, similar water to similar looking geos from the region, sveni for example-- most true Geophagus do well in near neutral, neutral, or pH anywhere in the 7s and temps in upper 70s to low 80s, I keep mine 78-80. I'd expect similar tankmates as other medium to large geos to work, I've seen them with Heros species. I've seen video where groups can be feisty with each other (while ignoring other fish).