Its ok use different layers for power?
For a 2-layer board its pretty common to have one dedicated GND layer and use the other layer for all signals and power. In any case, prevent long traces on the GND layer, otherwise you may have unnecessary long GND return paths (due to the split GND plane/islands).

For multi-layer designs, its good practice to have at least one 100% dedicated GND layer with no excuses. Regarding a supply layer it depends. If you only have one Vcc for example, use a dedicated layer as well. If you require 5V for one localized part of the circuit and 3.3V for another you can place those into the same layer (use planes, not tracks) if you have no spare.

Just keep in mind what you want to achieve: Short, low impedance tracks for commonly used signals (especially GND/supply). With dedicated layers for those signals, you just have to place a VIA.