My suggestions would be........
Buy the Battery Grip, I just got mine and I've fallen in love with it already.It really balances out the camera, plus the added controls are a godsend for portraiture. It's worth buying IMO.
I've been using the Pentax 50-200 lens on occasion as a portrait lens. Depending on the setting it's pretty good. And the 50mm f1.4 you mentioned getting is a really good lens for portraits. If youhave the cash to spend, the 77mm f1.8 limited is one heck of a piece of glass. I couldn't live without mine, but it WILL set you back some $.