Profile is important, you need to make sure you keep the edge square, or smiling, there should be a very subtle arc the entire length of the edge. What you certainly don't want is to get it frowning. You can either just start reprofiling, 800 waterstone is going to take a lot of time, and it looks heavy so a 400, or even 220 should be okay if you are gentle. The thinner the overall blade profile, the finer you want to keep the stones. That one looks pretty wedgey, is it a half hollow? I can't tell from the pic angle. If its near a full wedge, 220 will do the job. Courser hones may also leave more scratches from stray grit.
If you are worried about wear on the spine, you can tape it, but keep in mind the spine is supposed to wear as the blade is sharpened, so its up to you. Try to get as clean an edge as you can. Shortcuts don't really gain you much as the fine hones take nearly nothing off. After 4k, all it is is polish.
One note, its possible to get deep corrosion, you may have seen it referred to as crumbly steel. It will take a shaving edge, but under the lateral stress of shaving will go ragged again, so take it through the grits to 8k, and try to shave with it, just a patch, to ensure that you are in good steel. If it holds, then go finish it however you like.
Other options, you can breadknife the edge on a stone (use the end or a stone not needed for honing) and take the edge all the way back to good steel before rebeveling, if you are not careful, you can frown a blade pretty easily I'm told.
As long as the edge isn't crumbly, you should be fine, no need for files. (I am presuming you have a set of lapped hones for this little project?)
Hopefully this makes some sense, I've not done too many razors but I've gotten a few antique store gems to shave.