The level of rework depends on the current condition of the saw, and what you want to do with it. I have been lucky that all of my past backsaw projects started with saws that were not significantly bent, dented, or warped so that the work to the saw plate and spine consisted of simple rust removal and sharpening. They were reworked for use and not to return them to factory condition. I remove the handle and if necessary I wipe it down with acetone to remove any grease and loose finish, paint, etc. as required. I normally would use a fine abrasive pad to ease any sharp edges from past dents and dings just to make them more comfortable in the hand. A light coat of BLO followed the next day with paste wax is usually sufficient. I don’t try to and remove all of the rust staining from the plate. I think is sufficient to use a fine wet-and-dry abrasive paper and WD-40 to remove the surface rust and get the plate and spine slick enough to slide through the cut. After sharpening I coat the saw with a light coat of baby oil and then later I will give it a light coat of paste wax. The saw nuts are gently wire brushed and waxed. A drop of oil is applied on the threads when the saw is put back together.
I normally will sharpen the saw before I put the handle back on and I have come to the opinion that filing fine toothed backsaws with a rip style tooth is sufficient. I do ease the rake on the first inch or so to facilitate starting the cut. I believe that it has to do with the relative size of the tooth to the wood fibers. A sharp 12 TPI or finer saw used for joinery seems to work very well in both rip and crosscut applications and a crosscut tooth pattern seems inferior for rip cuts and produces no significant improvement in crosscut quality. It may also be true that the fact that I lightly stone the sides of the teeth after setting them may help with the crosscut action. Many joinery surfaces end up being hidden in the joint or end up getting reworked with other tools anyway. I prefer joinery straight from the saw when possible and have had no issues with joint failure due to saw surface texture. I lightly set the teeth and then lightly stone the sides of the teeth to even the set to about 0.003 or less per side. I really want the kerf to be only slightly wider than the plate and that helps to keep the saw running true. After making a few test rip cuts I will re-stone the teeth as necessary to keep the saw running true. Panel and carpenter saws have to be sharpened crosscut and rip because of the larger teeth and greater set used on those tools.