1. The game runs fine for me even when i get to levels 8 and onward.
2. The low number of time orbs is by design, in the game you have to master time saving with quick movements and decisions. Eventually though you're supposed to run out of time no matter how good you are , i did it this way to make each play-through fast yet challenging for all skill levels(at least this is what I've attempted to do), since you can try to just beat your high scores.
3. The coloring of the background is to make the level more navigable since there aren't many landmarks to orient yourself. Reversing the color order is probably a good idea though.
4. Levers open hidden rooms, if the walls seem out of place somewhere it may be a hidden room, hidden rooms give access to chests(no keys required for hidden room chests), these chests are guaranteed to give power-ups.