The link JPG gave you is a good start. Besides the document "Buying a Used Shopsmith" at the bottom of the page on Everett's google drive there are numerous other restored manuals and documents for the Shopsmith tools. As for using the Shopsmith check out the restored PDF version of the book "Power Tool Woodworking for Everyone" under "PTWFE 10ER 1953" also on Everett's google drive. It shows the Shopsmith Model 10ER in use. For the Mark V in use you can access a digital version of the current "Power Tool Woodworking for Everyone" book at the link below.https://www.shopsmith.com/academy/introduction.htm
As for which Shopsmith 5 in 1 tool to get the Model 10E and 10ER were made between 1947 through 1953. Being this old there are only 2 parts other than set screws and other common hardware that are still available. Those are the Quill Return Spring and the Quill Bumper Ring that are the same on the Mark V. The Mark 5 first went on sale in March of 1954 and later became the Mark V in 1980. The Mark V 520 is still available new today with a larger table and pro fence system than the original of the Mark 5. All Mark 5/V's are upgradeable to the current models of the Mark V 520 and the Mark 7.
With the Model 10's you are somewhat limited on what you can add to them as far as using SPT's (Special Purpose Tools) like the Scroll Saw, Band Saw, etc. Using these on the Model 10's requires a special bracket and pulley which are rare or buying a new fabricated one from Skip Campbell at MKC Tools. The Mark 5/V can use all of the SPT's.
I like both the Shopsmith Model 10E and 10ER tools along with the Mark series tools. I own and am keeping a 10E, a 10ER, a Mark 2 and a Mark V 520 that has been upgraded to a Mark 7. These are all useable tools although I rarely use the Model 10E which is one of the original 250 produced for Montgomery Ward stores in 1947 that started the Shopsmith success. I also restore Shopsmith tools as a hobby and currently have 2 Model 10's to restore plus my Mark 2. I may add additional Mark series tools to my collection in the future.