Be careful of rockwork on glass.
It prevents cleaning and traps detritus.
Pull it out a bit.
Otherwise great, enjoy your journey.
Welcome Hanna to R2R!
I will second the notion about rocks on glass. I like to be mindful of a perimeter of at least a couple inches in on all sides so I can effectively clean the glass there.
You may want to think about securing your rocks together when you settle on an aqua scape you like, just to be on the safe side.
I would move the rock in the corner to the white one in the middle and build a small cave or passageway, it'll give your fish a place to hide and they will be able to swim through, I would connect it from the white middle one to the purple rock.. similar to an archway. This will get the rocks away from the glass, as stated above its good to allow room for the magnetic cleaner to pass by.
If you don't want to get a refractometer, I would suggest getting a Hanna Salinity tester with the temperature gauge. I have one and it works good.
If you want to hide the tubes and wires behind it, you can get decorated backgrounds at almost any fish store or online instead of trying to paint it while there's fish, water and corals in the tank... probably not a good idea.