2: Upgrade Blink ASAP
This power allows you to instantly and silently travel short distances, uses very little mana, and is pretty much mandatory to complete any area unless you plan on waltzing through the front door and killing everyone in the game (don’t do it!). Upgrading Blink is cheap and allows you to travel roughly twice as far, so it should be one of your top priorities no matter what style of play you choose.