Welcome to
RP. I quickly checked the individual channels, and it looks like the green channel might be the best to work with. It's a good idea to check the individual channels when you first take a look at the job. In many instances, it can make things go much easier.
Most people who are advanced users will suggest that you scan the image at the highest optical resolution. This will not likely be the highest resolution your scanner is rated at, but the lower number mentioned. Higher resolutions do not add anything, but they make the files much larger. Never work on the original scan, but make a duplicate copy to work on. If needed, you can lower the resolution of the duplicate. But leave the original untouched in case you need to revert back to it.
Last, but not least, pick up a copy of "Restoration & Retouching" by Katrin Eisman. Most people on this site swear by the book. It's easy to understand, and makes things a lot easier. Good luck.
Ed P.S. I almost forgot, five meg files are not considered large files for most work. When you begin to add layers, that number can easily add up to *much* more than five megs.