Reptile leather is generally considered more formal, but it doesn’t have to be; it can always be dressed down. Buy from a reputable strap maker, not some random Aliexpress seller, to make sure you’re getting quality materials. Should you buy one? No idea…I don’t know you or your preferences.
A dress watch can be worn any time. It can always be dressed down.
The Longines can be worn any time.
I’d wear the Rolex with anything less than formal.
You mean chronograph, not chronometer. I’d wear these with anything less than formal.
The FXD is super casual. The others you could probably swing for business casual.
Anything missing is up to you and your own collecting goals.