Inspirations are the goals that pay for perks. There are 73 of them across 382 levels and 5 tracks, and each one is the same task at a rising count: craft five of a thing, then fifteen, then thirty. Completing a level pays experience into its track, and track levels are what let you buy perks.
A track level costs 2 experience, then 3, then 4, and 5 for every level after that. An inspiration pays roughly seven experience across all six of its levels, so one finished inspiration is about two early track levels.
Start with the free levels
The first level is free on 52 of the 73 inspirations. Taking every one of those costs nothing and hands over 52 experience, which is most of the way to five levels in every track at once. They are also goals you meet by playing normally, so the opening move is to read the list and claim what you have already done.
The tracks are not priced alike
Every track buys roughly the same number of levels, and the cost of getting there is not remotely the same. Farming reaches 18 levels for 254, while Smithing reaches 18 for 1,728. If you are choosing where to spend early, that difference matters more than which perks sit at the end.