Congratulations!
What a coincidence. I also bought a Pentax 645 (the II version) recently, and for the last five days, I've been shooting with it. I LOVE the camera! The viewfinder is so bright, and what a treat it is to have some automatic functions - like the film rewinds automatically after it's done.
I only have the 120mm macro lens at the moment, but what a lens!! I would recommend this one for portraiture as well - it also allows for some very closeups, like if you like to capture eyelashes of young children, etc., you can get in really close and do so.
I shot 6 rolls in the last few days (portraiture) but have not had a chance to develop them yet (can't wait). I actually used a handheld meter as for me, it is the easiest to use when it comes to portraiture and getting the skin tones right. I also am used to manual focus - with the viewfinder so big and bright, it's especially pleasant!
Please share your results once you have your negs developed!