Alex;
Hey! That looks pretty cool, to me!
I think you have accomplished a huge first leap in the DYI zimm world... from what I can see, you have indeed managed to get a pretty "in-scale" thickness (considering that real zimm coats were probably under 1.0 inch thick to highest relief, and maybe much less than that, based on looking closely at many pics... a 1/35th scale zimm coat should not be more than maybe 3/100 inch, and maybe only 10 - 15 thou - so as thick as maybe 2 pieces of ordinary copier paper!), and the carving and patterning look pretty nice, too. (Albeit you may well have the pattern "off" and maybe wrong-sized - no expert at all on this, remember!).
So, your zimm coat is, IMHO, pretty good-looking. I have seen (and, yeah, done) much much worse! Now - about the painting... I would point to your lower hull sides and note that you indeed have nicely picked the zimm out by darker grooving. This would do equally well for a start up on the turret (which appears to have some reversals! darker raised points and lighter grooves!). Where you did your white wash - I think it actually looks not half-bad! Again, the grooves would likely be darker.. (your biggest problem - looks like you pooled white down into those grooves... which would have both likely missed getting brushed-on ww, and would have collected dirt....). and if you did this, you may find that the overall worn ww effect would come thru nicely. It's a guess, but I think it likely...
IF you had a rear-deck / engine fire... probably there would be some sooting up the adjacent turret side(s)- this blackening (soot, from smoke, as versus suggesting a roaring sheet of fire) would fuzz over that zimm and its paint layers. So, first doctor up the zimm to get it looking the way you want it to for a faded ww coat over your camo (keeping in mind that notion of darkened grooves and dirt / grime collecting down in them) - AND THEN do the sooting over that.
You can certainly mist it on as a thin soot-grey wash with an airbrush... or...
It might be worth a little experiment (maybe do this on a piece of wood with some zimm applied and painted in all the layers - a sort of crash-test dummy before you try it on the styrene kitty...): take the soot target out into the outside air, create a smudgy smoke-bomb type "fire" (a candle, a few pieces of sprue propped into the flame to smoke nicely), and coast your soot target thru the higher smudge cloud. Do NOT get too close to the fire, and do NOT hold the target in the smoke trail a long time - no heat build-up is desired!. A few passes could well create the sooted look you may want. IF I were trying to soot my turret in your scenario - I would strive to get the turret bottom edge into the lead in the smoke, and let the smoke crawl up the turret side - sooting the zimm as you go. NOTHING looks as much like soot as does soot!
IF you wanted a major roaster fire look - you would need to really rust up those plates which had become incandesent hot - burned off all the paint (and the zimm) and creates lots of brighter rust. The gradient edges around those hottest areas would be blackened, as where the paint and zimm partially burned off.
All in all, it looks like you are off to a running start on all this!
I don't have any links or citations to give to you - but I would maybe cruise around this site and over on FineScale Galleries and / or Track-link galleries and look for some "burn-out" builds and see how folks have done their camo-to-ash and rust gradients. This look - see could give you lots more effective guidance and inspiration than verbose ol' p-bob can give! (Not that I mind blathering!

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Cheers!
Bob