You are at the start of an incredible journey. And you are certainly off to the right start by focusing on researching and learning. Knowledge truly is power.
While I am generally not one to offer advice to anyone as to how they should do something I am happy to share what has worked for me since I bought my first vintage watch 35 years ago. These are the factors that are important to me:
1) Condition, condition, condition - I am a condition fanatic. For me this means an unpolished case, a dial that is original and has had no restoration work, an excellent condition movement. I want to see the watch in person. If not possible I want to see multiple high definition images of outer case, inside caseback, dial and movement. Many collectors like a watch that shows its age. Makes sense to me, but that is just not what I choose to do. While it is extremely difficult to find watches that meet my standard I try to be patient for the right opportunity. Fortunately, sometimes I have been lucky.
2) Research - Before buying or bidding, I will check the data bases of the 4 major auction houses for prices realized, watch descriptions, history of the reference and if still available condition reports. Also I might find the specific watch having been previously sold. Have any changes been made to the watch, eg a different dial which would be a disqualifyer? What did it previously sell for?
3) It’s all in the details. Rarity of the reference, rarity of the metal (eg a steel 1518 is worth many multiples of a YG 1518), rarity of the dial.
4) My general rule - If in doubt, I pass. I am OK overpaying a bit for an incredible example, but buying a mistake eg a watch that is incorrect can be a disaster.
5) I go to as many auction previews as possible. Nothing like examining watches in the metal to expand one’s knowledge. Plus it is great fun. Like going to an art museum.
6) I have and continue to read many treatises and auction catalogues (with prices realized).
7) I have to feel confident in the seller. If I have any doubts I avoid that seller no matter the temptation.
Last comment - I find buying great modern Pateks (which I also love) is relatively easy in ordinary times ( of course we are not living in normal horological times right now) if you have the money. Buying great vintage is much more challenging and in many ways much more rewarding.
So wishing you good luck on your journey.
Best, Patekova