f5 ?

b) I'd say that the white pieces are still very slightly more active and the black pieces somewhat uncoordinated. Most significantly, the black king is still in the centre. I think this is the determining feature as after, say: 1. Kh1 0-0 black seems fine and about to improve his pieces. Further more, the Bc1 is still stuck. Therefore: 
 
a) 1. f5 
 
This was first just a hunch, but it seems either captures is really bad (but I moved the pieces): 
 
1. ... exf5 2. e6! Ne5 (seems safest) 3. exf7+ Kxf7 4. Bxf5 (a pseudo sacrifice opening up the king with a big initiative.  
 
1. ...gxf5 2. Nxe6 fxe6 3. Qh5 + Kf8 4. Bh6+ Kg8 5. Bxf5 and this shoudl even win. 
 
1. ...0-0 since white can't take, he should either castle into security or try to bolster e6. 2. f6 seems interesting enough though complicated after the next few forced moves: 2... Bc5 3. Nxc5 Nxc5 4. Bc4. This might be the best for either side. 
 
1. ...Nc7 The defensive option, but after 2. fxe6 Nxe5 3. exf7+ Nxf7 4. Bc4 Black still has chance for an attack.