The standard option for a shop floor is a concrete slab. You’re probably not going to go to the trouble of creating a basement beneath your shop, although it is possible. The weight of most woodworking machines suggests that a concrete floor is the most solid and durable substrate available. It has the potential to be used as thermal mass to store heat from your heating system or from the sun, but it can be tiring and hard on your body to be standing on concrete all the time. You can add a vapour barrier, 2x4 sleepers and a wooden floor above the concrete to ease the tendency of the floor to strain your feet and back, or you can add anti-fatigue mats in key areas where you’ll be standing for longer periods.
Softwood is most commonly found in the regions of the world with lower temperatures and is typically less durable, lighter in weight, and more vulnerable to pests and fungal attacks in comparison to hardwoods. They typically have a paler color and a more open grain than hardwoods, which contributes to the tendency of felled softwood to shrink and swell as it dries. Softwoods usually have a lower density, around 25-37lb/cu ft, which can compromise its strength. Density, however, does vary within both softwoods and hardwoods depending on the wood's geographical origin and growth rate. However, the lower density of softwoods also allows it to have a greater strength with lighter weight. In the United States, softwoods are typically cheaper and more readily available and accessible. Most softwoods are suitable for general construction, especially framing, trim, and finish work, and carcassing.
I have never worked with my bench up against the wall, because I like to work from all 4 sides of my bench. I do like my machines pushed up against the wall and a large open space in the middle of the shop to facilitate easier movement. I have a Minimax combination machine so by necessity my tablesaw and jointer/planer are bundled together but I would actually prefer they not be (like a Felder machine that breaks apart). I would never put my tablesaw central in my shop, always at one end with a clear entry and egress for the sliding table, space permitting. Putting a tablesaw in the middle always struck me as one thing I’d always have to walk around and/or fight the temptation to stack stuff on it.
Unless you’re a big fan of frequent shop remodeling, planning the layout of your workshop early in its development will save you a lot of time and trouble and also can keep you from spending years in an uncomfortable, poorly organized space. And if you already work in a shop that’s as organized as a trailer park after a tornado, careful planning and a little remodeling is likely to help you make a quantum leap.