You asked about grossa initially, which is looser than fina. Comparing fina to piccola, I would go by what it says on the website. FWIW, I have both piccola and fina ties from Hober and it is very difficult to tell the difference.
If you look at some of their newer offerings, the Carlyle for example, they have some more "aggressive" styled shoes. That said, I disagree. While shoes with such styling look great when posted in pictures or standing on their own, I find they do not look as great when actually worn. The long pointed lasts or long chiseled toes just don't look that great, especially if you are bigger or of muscular build.
This is all of course my opinion.
I was just in the store the other week and I have not been impressed with Burberry's quality lately. Admittedly the prorsum line is a significant cut above, but I believe it is overpriced for what it is. You can find equal for better quality at a much lower price elsewhere. The charcoal tuxedo from Mr. Porter is admittedly kind of cool, but not something I would look into as a first or only tuxedo. Go with your gut, go with black and go with shawl lapels. Shawl lapels...
Visual, there is basically no difference. The colors are the same. The only semi-visual difference is it says "Brooks Brothers" on the footbed instead of Allen Edmonds.The shoe itself is the same construction, except that the BB version has the poron heelpad. This makes the shoe fit a bit smaller over the arch and your foot doesn't "sink into" the shoe as well until the pad is worn in. Whether you like this feature or not is personal preference.
This depends on how much you really care. Strictly speaking, shell cordovan is a more casual leather and many on this forum would not consider wearing it with a a suit. Also, saddle shoes are bluchers (compared to balmorals) and considered again more informal. Ideally not worn with suits. saddle shoes are probably more informal to boot.
Now, realistically speaking, no one will care outside of a few select individuals you're unlikely to encounter in daily life and...