Painting process for wood steps

Ok, so I should have posted earlier if I wanted this info, I guess. But, here is where I stand. I have a set of four wooden steps that go from the main floor of my house down to a side door, and then more steps proceed down to the basement. I am simply repainting the wood steps because the previous homeowner had attempted to paint "stones" on the steps, which we didn't find too convincing or desirable.
So, I spent a very good deal of time sanding with several grits of sandpaper on my random orbital sander. I did some paint removal with those paint stipping drill attachments just to speed things up a bit. I didn't want to sand down all that far, but I realized that there was significant residue (for lack of a better word) from some rubber stair covers/runners that had been there before (they are still on the stairs that go the rest of the way down.
So, if I wanted anything resembling a smooth finish, I was going to end up sanding down to bare wood. So, I did. There was some paint remaining in some spots, particularly on the vertical surfaces, which I could not power sand, but I did a decent job sanding them by hand, I think. So, this morning we used a latex-based primer to do the first coat. And, we are in the midst of waiting to put the enamel latex top coat on. My question is what should I do now (and I really hope that you don't say start over)?
I would prefer not to have the brushmarks show up a significant amount, but I am thinking that they will. We bought good brushes, but they are still pretty apparent. Should I sand before putting on the topcoat? Should I put one topcoat on, sand, then do another coat later perhaps? Should I consider switching to rollers? And, if I am going to sand down the primer or any other layer, how long should I wait before sanding? It says to wait 4 hours before putting on another coat. Does dry enough to put on another coat mean dry enough to sand also? And since these are stairs, not walls, does dry enough to put another coat on also mean dry enough to walk on or no? If not, I am going to have wait a while longer to get this next coat on.
I hope that someone can answer me somewhat soon, as I really want to approach this the right way, after spending many hours striping and sanding.
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