If you work with rough lumber, a planer will be absolutely necessary, except for the most rustic of projects. Every piece of rough cut lumber ends up somewhat not straight, not flat and not consistent in thickness, either from variations during the sawing or from stresses which occur while the wood dries. The planer, combined with the jointer, is a one-two punch to remove these variations and produce straight, flat and consistently thick lumber. The reason the planer is ahead of the jointer on this list is that some lumber is straight enough and flat enough to plane without jointing if the job is a little less finicky, thereby skipping the jointer.
When customers visit my shop we usually start by talking about their wood needs. If it is someone’s first time to visit I also try to get to know them, what they are looking for and what they are expecting from me. Half of them are just looking for rough cut wood, while the others are looking for wood that is processed a little bit more, perhaps jointed or planed, or even sanded. During our time together I get to understand their needs and abilities, and our discussion usually turns to the tools they have in their shop.
Let’s be clear about one thing: No workshop is perfect for everyone. If there were, I could simply give you a precise plan to follow with clear dimensions. Every person who comes to the hobby, avocation, or profession of woodworking has his own particular collection of tools and his own peculiar work style, skills, and desires for the kind of woodworking he wants to do that gives him a unique approach as to how he will lay out a shop: where the tools should go, where lumber and supplies are stored, and how much bench area he needs.