To me, a collection has a theme. What many here call a “collection” is just a bunch of watches we like to wear and have bought over time. So, to answer your question, I will give you some collection ideas where you could accumulate quite a few watches (I think) for the $8000 limit. Then ideas for a bunch (or a couple) of watches you could wear daily for years to come.
True Collections with a Theme:
1. Watches of the Vietnam War: there were lots of different styles available in the PX that American servicemen bought and wore. Most can be found for under $1000k: Glycine Airman, Ollech & Wajs Early Bird, Zodiac Sea Wolf, Seiko 6105-8000, Benrus field watch, etc.
2. Watches worn in space: of course there is the Speedmaster, but there are dozens of other brands. Go even further and limit it to watches worn on the moon, and there are more than the Speedmaster. Getting more than a one or two would probably blow your budget, though.
3. Watches worn by James Bond in the movies: lots of choices here, some Omega, but also Breitling, Seiko, and even Rolex.
Lots of other ideas there, but you see what I mean by a “collection”.
Watches to wear that don’t really have a theme:
If you just want a variety of watches to wear, get an Oris diver, a Longines dress watch, a Valjoux 7750 Chronograph (any brand), a Seiko diver for a beater, and then treat yourself to a nice vacation with the residual.
Or, if you want to focus on Omega watches, buy a used Speedmaster and a new Seamaster 300m and call it a day.