Instead of "fiddling endlessly in photoshop" I recommend that you do something quite different, which is to produce a full charcoal piece. I would work on grey paper, using charcoal or conte, and a stick of white for highlights. decide what you are excited about, and begin to sketch from your reference image making sure that this element takes front stage, as it were.
using charcoal or conte on their sides helps at lot, because you can quickly smudge and move things around with your fingers.
Make sure that you work to the same aspect ratio as the canvas you plan to use.
Importantly, work a fair bit bigger than your photo
. Even better, do it the same size as your canvas.
The difficulty, often, with scaling up from a photo is that some shapes seem to become sort of big and empty when you "grow" them so you may need to use your imagination a little, to make the shape more interesting - thinking about the brushwork can help, and also making the colour more interesting by varying it more than the photo information is offering.......for example, a grey patch of wall in shadow in a photo might look ok, but as a large area of a canvas, if you paint it all one tone of grey, it may look really boring. However, vary the greys -blue-grey, pink-grey, purple-grey, green-grey, all in the right tone value, and suddenly that area of the image becomes far more interesting.
Doing a preliminary piece to the same ratio, a fully-realised charcoa tonal preliminary ( not just a line drawing), will prove invaluable, I can promise you that.
Here is a charcoal sketch I just found quickly on google: it is a good example of something fairly loose, no fiddling with detail, no clinging just to the outline... the pattern of tone is all there so this would be good to work from in colour.