Someone reincarnated into the shire with a library system, a normal library but with a power to make books for others, not just normal books but every time they write a book or comic they can write skill books based on those in the books. When using a skill book you would have a basic mastery of that skill and the relevant knowledge for that mastery, the librarian will master the skill's to the highest possible.
Skills have grades and mastery levels, while people other that the librarian are limited in the amount of skill books that they can use, for example merry can use up to 7 where as Frodo can use 10 and Aragorn can use 20.
This limitation is only for different types of skills, if you first use a skill book called stealth, than any number of skill books that connect to stealth can be used. If you use a skill book way of the king then many skill books a king may need can be used.
There are no restrictions on mastery skill books for example if Sam was to get a book on gardening but it was only at basic mastery he could use as many gardening skill books as he wants without taking up any limited spots.