As far as cotton augustus, anything seen as soft and airy as "cotton" has potentially demasculinizing qualities. Imagine it ... A six foot tall man in a suit comes up to you, clean cut and athletic, and says hi, i'm cotton, i'm going to be your attorney.
It's creative, but would work better for a girl.
I personally wouldn't immediately shorten bartholomew to bart, since it's a slightly unusual name and people probably aren't as familiar with the preferred nicknames (katie from katherine, etc.), but he could easily introduce himself as bart or barth without any problem.
Cornelius henry wouldn't really need a nickname, although you could get away with neil. Take note, it does sound a bit old-fashioned, but if you're looking for a classic name it's not a bad idea. Beware the nickname corny.
Octavia rosemarie, cordelia blanche, and flora anneliese (or flora bernadette) are all lovely names, although blanche does come off as a tad ... Bland.
Just my opinions! Good luck!