I uses to buy cheap Seiko watches that were not working and gently investigate. At the price I was picking them up for you could afford to buy a few of the same type, and usually build yourself a nicely working watch at the end of it. India was a good source of these; they had cornered the market on cheaply repaired Seiko that seemed to keep time for a few days then go haywire. I learned quite a lot from those. After a while I started buying broken higher end but unfashionable watches, like 1970s Omega, and doing the same thing. Ladies high end watches are brilliant for practicing on as they tend to be a fraction of the price of the Mens variant.
It all changed when the 1970s Omegas suddenly became fashionable again, so I sold the lot and bought a modern one that I don't (and won't) touch. It was a good fun learning experience. I wish you the very best of luck.