Sgian Dubh
"Would you dress the lumber including whatever is necessary to flatten it and take out any cup and twist first and then resaw it ..."

Yes, that would normally be the best approach, particularly as you don't have a great deal of material (thickness) to spare. I'd do no more than is needed to get both faces with flat spots parallel to each other, meaning there may well still be some rough islands in between the flat parts of each face. Also, square an edge to the faces to run on the bandsaw table.

However, don't be surprised if the resultant two boards from deep ripping need to be flattened and thicknessed again because of subsequent warping through stress release caused by the deep ripping operation. Hopefully this warping will be minor, and further flattening will result in thicknesses you can use ... I refer you back to taking off as little as possible of the original board as described in the previous paragraph.

That's a good result, but the risk with deep ripping (resawing) is that you release significant stress within the original board, which could mean that the two resultant boards are essentially unusable. You could test for this possibility prior to deep ripping by undertaking the fork or prong test. This test, admittedly, primarily shows if a board has, or is free of transverse stress rather than longitudinal stress: but, more often than not, if a board has one form of stress there's a very good chance that it has the other. Slainte.