Paint it Black! (channeling the Rolling Stones for you youngsters, lol). The "golden rule", (just to slightly disagree w/Wild West), is more like 3/5 for your focal point (wood, rock or major plant.)..but 1/3's are good too. Just don't do 1/2 and 1/2, it looks really lame & artificial.
I would suggest not mixing those 2 types of "wood", nice as they both are. It can only look forced. Rocks hopefully will echo your substrate...too much contrast is off-putting unless it's by color...to me anyway.
I'm the same generation, Fishorama! CAUTION! Wall of text below!
I am already second-guessing myself on the petrified wood anyhow....it in no way matches the oil-dri substrate, which is a kind of grey/white, darkening with age. As you can see, the petrified wood is tan/brown.....I'm not an interior designer, but those two colors don't appear to be complimentary, especially when you add the dark brown of the Mopani. I guess I can always go with the assumption that after I mess up the water chemistry everything will be shades of green, the difference in color of the substrate/petrified wood/Mopani wont matter....but, what happens in the infinitesimally small chance that I actually succeed and they DON'T become totally covered in 10 different species of alga and diatoms!? I AM going to use the Mopani, because I like it so much....the piece I got was relatively cheap....under $18 (still need more stuff, like ferts and a Cu test kit), I can get another to take the place of the petrified wood. I have plenty of time to soak yet another piece....the first one I am soaking is almost done...after several water changes in the tote, the water is nearly clear.....not as bad as the horror stories I hear in some Mopani reviews!

Currently, I am at 5 coats of urethane on the stand, hinges on order, so, I expect THAT to be done by the end of next week....then have to get my son to help me carry that monstrosity up from the cellar. And the aquarium from the cellar...hope it fits! I do like the "paint the back" idea, I will mask and tape it today, using black spray paint to do the job prior to putting it on the stand. I really cant envision a situation where I would want a clear background anyhow, since I abhor looking at pipes, hoses, cords, etc.
Am researching plants.....WAY back in the Stone Age, when I kept freshies, I always had huge luck with Anacharis and Cabomba...so much so that I still recall the cleanups from them...like raking leaves in the fall (if you're from New England, you know what I mean!)! They grew like mad and I am afraid to use them again, because of them shielding the rest of the stuff. Heard nightmare stories of crypt melt....that'd be me.....I'm liking sag and swords (yea, root tabs, I know!), java ferns and moss, and am also looking at low growers....don't really want to cover the substrate completely, anyhow.
Ferts? To start, Seachem Flourish, Nitrogen, Trace, Potassium, and they also make a root tab type of product (Flourish Tabs). I will be injecting CO2, controlled by the pH probe and meter, and am still fussing over LED lights atm. Fish load? Just a few guppies at the start (why I am looking at Seachem Nitrogen)....eventually getting Otos, shrimp, and Nerites. I am just concerned that cycling with my plants will be not a typical cycle, and don't want to endanger any more lives than possible through the cycle.
