I struggled with the same question when I started diving. Here is what I have learnt:
Classes should never be taken consecutively. In other words, after getting an OW certification, I would do at least 20 dives before taking the Advanced Open Water. The material learnt in a class should be followed by a lot of individual hands on before something new can be added. Skills taught in a lot of courses like peak performance buoyancy, boat diving etc can be learnt simply by more diving. Advanced courses then can be reserved for what needs to be learnt under supervision such as Drysuit and Ice diving, drift diving, underwater photography etc. Those are REAL courses in my opinion and not an attempt to pull cash out of a new over enthusiastic diver by teaching him what he should know after an OW course or what he is bound to pick up from experience anyway.
As for gear, I do not believe in buying most gear right in the beginning. If anything is to be purchased it should be wetsuit mask and fins as fit is important in those. All else should be rented and tried out before one realizes what type of gear they prefer.
All the best my friend!
Very logical advice. I always wondered why they had a "'perfect' buoyancy" class, and I would rather get something a little more tangible if I'm shoving boatloads of money at them.