I didn't buy the official walkthrough so I couldn't tell you how detailed it is, though you can take a glance at the store page to get an idea. But no, the wiki pages and the linked google document of community tips should be enough to get best endings and a majority of the content. The official walkthrough is basically a hand-holding guide, while the wiki+google doc is a general overview. If you can't afford the walkthrough, you're not losing out on much.