please move this if it doesn't belong in this section

I am brand new to wargaming in general & i have decided on WH40k.
I have painted a squad of Grey Knights, and they interest me very much.
Unfortunately,after my first squad, i am having a bit of trouble deciding my next move, Should it be an HQ choice, a transport like a razorback, or another squad?
Thanks in advance,
Spark.
P.S. I have a strike squad, not a terminator squad.