You will receive many different answers to this question. However in my view they will all be completely irrelevant to YOU.
There are no correct or incorrect answers. I imagine that many of us came to the hobby randomly.
Like a watch. Buy it.
Decide you “need” another watch for variety. Buy it.
Ah two watches aren’t enough. Buy another one.
You discover another style of watch you hadn’t considered. Perhaps you have been happily swimming whilst wearing one of your watches with 100m WR. Now you read that you “need” a dive watch for swimming. Buy one (although very few people actually need a dive watch!).
Oh I don’t have a dress watch. Yes I know I will only wear it 6 times a year, but I need one. Buy it.
Oh look a chronograph. Most seem to have one. Buy it.
Or many other variations of the above. Bit do you really want all these different types of watch? Only you can decide.
Many people have multiple watches from their favourite brand(s). They may all be of a broadly similar style. Add in a few other watches from a limited number of other brands, selecting different types of watch. Now that may well be my approach to collecting. Job done!

Just go with the flow. Buy what you like. Set your own limits. Be prepared to change. Ignore what others say about what a collection should consist of.
The only views of others that are relevant are those that come with the benefit of ownership or handling a watch. Even then that is only about that particular watch, not whether it is right for you.
Neil