Ditto the answers above. Not an expert but have sold some over the years that have accidentally come my way and certainly have seen plenty "sell" over the years at B&M auctions. Buyers on eBay expect to be able to know and see exactly what they are getting. If you check eBay Sold it is easy to see that those combos of MUH that equate (roughly) to useful posting values sell most quickly and at close to the 75% face value suggested. Like 50c + 22c, or 45c + 27c, or 85c + 55c. Mixed values will achieve less. FDC - well, I am sure there are some valuable ones out there - not being an expert I don't know about them. All I know is that there are lots on eBay  - about 20,000 at a quick glance and that only about 20% of them seem to sell, and most for around $5. If you know / suspect you have something valuable, do a quick search, but do look at SOLD items.

 As for your stock books, and stamps on paper - again, unless you know / suspect you have things of uncommon value, you might be better just putting them in a B&M auction sale in a plastic tub. I see oodles sold like this quite regularly, but at least they sell (unless the vendor has some ridiculous reserve.) The dealers at the B&M auction will be able to sift through them, and they should achieve their value. Selling used stamps and stamps on paper on eBay can be very time-consuming and quite stressful. If you were the collector so you should know whether what you have is run-of-the-mill (so only worth a % of face value for MUH and not very much for your other items) or something better. If something better check sold values and good luck.