I'm glad you like my bike (some of you like it so much they want to steal it :-)
I bought the bike already modified so I'm not going to know all answers but I'll try.
Yoshis - I love the pipes, great sound, super light
seat - yes, it is Corbin, probably some older model (the bike is 2002) with carbon fibre efect. It fits, feels, and looks better than stock but it's heavier
covers - they are CF but there is no brand name on them so I don't know what they are.
The guy I bought it from had no problem spending big bucks on his toys (Audi A3, Ducati 998 ...)
I got the bike pretty much for the price of the stock one :-)