I often play similarly with Black, I'm a much weaker player than your opponent though. Still, I find I sometimes have problems when white castles long and goes for a pawn push, so this seems like a good strategy here.
Here's a game of mine (warning: game in progress) Game 5809007
Not sure how much the fianchetto makes a difference though.
. Black aims for counterplay which usually means trying for a queenside counterattack. Black used to castle quickly but now quite often delays it to a) remove a target for White's forces and b) be able to accelerate his queenside attack quickly.
A) WHEN BLACK CASTLES QUICKLY
White's main kingside advance in the Velimirovic is to advance his g-pawn, but in some circumstances he may use other strategies should Black handle the defence in an uncommon way.
White's light-squared bishop supports a number of piece sacs on d5 and is also useful defensively.