Default [Q] Flashing themes with safestrap?

Is it possible to flash themes on to a rom slot with safestrap? Im not sure if flashing themes is allowed with safestrap since some stuff are locked down.
I want to flash this -> onto my rom slot 1. AOSP is really cool !
Also, whats the "normal" amount of ram a person should use? my s4 uses about 1.2 gb when I don't even do anything