I've not used the F5, but if its electronic rangefinder is as good or better than the one in the F4, it will be extremely helpful for manual focusing. Unless you find blinking LEDs disturbing or annoying, which some people do. The type J (microprism) focusing screen seems much easier to find than the A or L (split prism) screens.
I too love the 50mm f/1.8D. I often find myself using it instead of my 50mm f/1.2 AIS, which makes me feel slightly guilty. It's small and light, it's cheap enough that I don't worry about getting it wet, and most importantly, it's just a really good lens. It's better than the 1.2 for macro, either by using extension tubes or reversing it (I'll often pop it off and simply hold it backward over the lens mount with my left hand).
Regarding superwide lenses, I LOVE them. But it does take practice to learn how to use them. I recently went through a 6-month slump where I didn't take any photos at all; when I went back out with my 18mm, I found I had forgotten how to use it! It took me a few weeks to be able to properly "see" with it again.