My opinion about your questions:
1. Watches are an individual thing. Some men are watch guys like some men are car guys. If you are into watches buy something you personally like that suits you. My BF used to wear a gold Rolex (when he had his Viper) but he no longer wears a watch at all and doesn't really miss it. My ex wears a Swiss Army black and silver chronograph that has kind of a diver look or a Tag Huer look but much less expensive to purchase that looks great on him. He's a watch guy. Wearing a Cartier gives a different vibe than a Tag which gives a different vibe than a Rolex, and there is a difference between a gold Rolex and a stainless one. Totally a style thing so pick something that goes with your own personal preference.
2. Basic Bermuda shorts are best for giving a stylish image in South Florida. Don't buy cargo shorts with 6000 pockets. Those look sloppy for going out and about. Check out J. Crew or Ralph Lauren for shorts. Khaki, Tan, Navy are basics. White can be good in the summer too once you get navy and khaki bought. Shorts can be fun. Go to a good golf shop and look at the sort of shorts they carry. You can have some fun with shorts if you wear a fun print or a plaid with a solid t-shirt or golf shirt. Again, based on your sense of style. You can't go wrong with solids but one plaid or print might be fun. Google Palm Beach Casual Men's Style. That's a good look. You'll see various things there that say "sophisticated" in a relaxed way.
3. Polo shirts are fine. Golf shirts are fine. Take cues from high end golf shops for example as far as what's in vogue locally. A couple of linen or tropical print short sleeve shirts with solid shorts, jeans or pants can be a good look. Look at how the men dress in the TV show Miami Vice (both the current one and the original one). Those guys were classically stylish in Miami/Florida tastes and even though the original show was on years ago much of the style the guys wore is still in fashion in Florida...perhaps a little tweaked and updated but you'll get the idea.
4.
@R.U.G. covered pants pretty well including jeans. Again it depends on your individual tastes and style personality. My BF wears Rock Revival jeans almost exclusively, but my ex hates Rock Revival as he thinks those jeans are too blingy and flashy. They suit my boyfriend well. My ex wears more the Lucky brand jeans or other less ostentatious things.
5. Instead of running shoes wear some Vans or some Adidas Sambas. You can also get a nice pair of leather or canvas flip flops for very casual wear in FL. To wear with shorts and a t-shirt for example. Some clubs won't admit you in flip flops so keep that in mind. Also, if you wear flip flops, pay attention to your feet, and in particular your toe nails. Toes nails should be neatly clipped and clean at all times. Get an occassional pedicure (seriously). If you have nasty yellow thick (nail fungus) nails, don't wear footwear that shows your toes. If you have attractive feet, you can wear footwear that shows off your feet and you'll look relaxed and cool.
Hope that's useful & nice to see you back.