Here is another take on some of your questions; based on my twelve year's experience with my current bench:
Like Tom, above, I employed a split top design for two reasons that were important to me: I like a tool well. The well holds the hardware that I often use such as bench dogs and some measuring and marking tools. Most importantly (I never anticipated this), having the bench top in two pieces makes handling of the ash bench components just that much easier if you ever have to move your shop. Think of it like the story of the guy who builds a canoe in his basement and then can't get it up the stairway. My bench would not, in fact, fit into the basement stair well; yet I assembled by myself it after a move a few years ago.
The bench legs and frame have bolted components as well; for the same reason. The two leg assemblies are an H configuration with glued M&T joints. They are draw-bolted to the two rails.
Good luck on your build! A good bench is a game-changer.