it looks like you have pleanty of big rocks.... what u can do is kinda stack the big rocks lower then get some more LR some smaller and not so round shaped ones.... then i would carefully stack those rocks giving it a random look ....
meaning place bigger rocks at bottom of sand bed..... then stack others of random shapes higher in the tank till they lean back to the back of the tank touching the glass giving them support and making them steady.... this gives it more of a 3dimensional look instead of a flat pile of rocks........ key to your tank is getting more smaller random LR
hiding equipment is tricky nothing you can do with powerheads really... what a lot of people do is paint the back of there tank with a flat black paint so that the tubing and powerheads blend in better.... blue back grounds are nice but they make the equipment stand out more.... u can also stack rocks to kind of hide certain things like heaters....
my tank is not in my room but the 2 fluval 404 canister filters r not that loud.... the only thing kind of annoying to me are my 2 3" computer fans in the hood used to cool down my 470W of pc ....
i would go for some PC lighting for your tank with a mix of actinics and 10K daylight gets rid of the purple effect .... u should be able to find some kind of retro kitsonline that will fit the size of your canopy just do some searches.... i would try to get a kit with around 200watts of power
as for corals... as long as your parameters are good i would start off with some polyps&mushrooms they are easier to take care of try those for a while and see how they do... when u want some other corals test your calcium u will need correct levels... whatever your interested in you should search info on it online first to see what requirments that specific coral has.... but mushrooms and zoo's can handle lower light cond.
heres a pic of my tank which might let u see how i stacked my rock.... i have some bigger pieces at the bottom for support then some other random sizes placed to creat a ledging effect.... everyones got there own taste just play around with it... good luck!!! :happyfish