T am a long time GS1 USer and I love it. I am over-camera-ed and the GS1 is one of my most favorite ones. And yes you do want a grip. For Sure the grip. if you want to shoot verticals you have to rotate the camera and it is heavy so the grip really helps a lot there. The 100mm lens is a super performer. I did a trip to Maine with the GS1 as main shooter and it did very, very well. Results can be seen on my web page at loganphotographics.com.... have fun... I know you'll love it.
Logan