I took the do everything together approach. I kept all classes with 10 levels of each others. This did significantly slow me down from reaching the end game but when I finally reached it, I was completely versatile.
What I recommend, level your main class to 50 and supporting classes for cross class skills.

CNJ/WHM to 50
THM/BLM to 26 - Swiftcast
ACN to 34 - Eye for An Eye

Leave crafting until later. The reason for this is, as a healer your gear requirements to be effective are the lowest of any party. The game gives you gear for free as you progress through the Main Story Quest (MSQ).