You would eventually need a daily beater (Casio/ Seiko), a dress watch (be it stainless steel or precious metal, with leather strap and thin profile), a diver (date or non-date), a rather casual watch (like GS Snowflake/ Rolex Explorer), a travel watch (GMT or Pilot watch), a chronograph watch, sometime you might wanna try out digital watch (smart watch) or quartz watch (can be just as expensive and luxurious like the others Swiss Made counterparts).
That being said I only use "a", you could probably own two divers or even more watches within same categories.
Conclusion, you still think one is enough?