I have little experience with outboard bearing BB's so I can't really recommend one over another. I have installed and briefly ridden both FSA and Shimano systems though and didn't notice any significant differences. Personally, I'd pick a crankset I liked and use the compatible BB (included with the crankset on some models). Or go Googling for reviews.

The cranksets that work with the outboard bearings are designed such that the chainrings are no further outboard than with a standard BB. Your front derailler will continue to work properly as long as you stick with a double/triple (whichever you started with). Some of the newer deraillers are only designed to work with specific chainrings but in my experience, older deraillers are much more accomodating.

Take your frame to the LBS to have the BB faced if you are concerned about squareness. They should have the tools to properly machine the BB surfaces parallel. To properly check the surfaces would take just as long as it would take to have them faced. You'd need to somehow locate the centerline of the BB shell and get it perpendicular to a known flat surface. You could then use a dial indicator and check the height around the circumference. I wouldn't bother.

You shouldn't need any spacers. As far as I know, Italian BBs only come in one width unlike English BBs.