Congratulations! Its a lovely lens and definitely one of my favourites.
Optically FA 100 is better than most other lenses in the range (that I have used anyway) because:
1. Its sharp across the frame at most settings
2. Basically zero distortion
3. low CA
4. Pretty sharp even wide open at f2.8 (as long as you have the focus right)
5. Its a 1:1 macro so at minimum focus distance you see a lot of detail!
I find the focus limit is brilliant and is something that is missing from later DA macros. Macro lenses have a longer focus travel (from a very close focus distance through to infinity). You limit in two zones (just roughly focus then set dial to "limit"):
- Close / Macro focus
- Normal telephoto distances focus
When using the limit the auto focus is much faster because it does not have to hunt through the whole focus range. So if you are doing normal telephoto work (or even portraits!) set the limit focussed towards infinity and its auto focus performance is better than later macro lenses.
The clamp can be useful. For normal AF work set it to "Off" (less work for AF to do). When using the lens in Manual Focus it can be useful to set the clamp to on because this gives manual focus ring a better feel (damped) which makes it a bit easier to focus.
Have fun!