Right um yes skills do have requirements such as being seated and so on HOWEVER. A seated officer can master up to 1 of the 4 areas but they MUST learn all skills one after the other to do so. 

A lieutenant can master up to two areas at most. 

Captains can master up to three 

And head cap'n can master zem all xD 

Basically im applying the Ikkaku theory here. He is a master in Zanjutsu despite being seated (he fought insanely well against Kenpachi who is himself a master) so yeah seated officers can master up to one area only...