Here's my first go at a textured section of (scrap) wall for my 'Dura Europos' walls, which I've also painted. The 'stonework' was modelled by 'peeling off' the card from a patch of the foamcore and replacing it with some embossed PlastiKard. The 'render' was a thick painted layer of B&Q's own brand textured masonry paint, painted on, and then with water 'floated' over the top to even out the worst of brush-marks.
Three colours - all Vallejo Model Color. 912/122 Tan Yellow, splurged on all over. 837/007 Pale Sand, drybrushed lightly onto the stonework and 'scrubbed' heavily on the render. White, dry-brushed fairly heavily on the render.
I think it all works reasonably, but I may well pick out 1/3 or so of the stones with a couple of different coloured 'filters' to make them look less uniform and more stone-like.