Welcome to the forums, Ben!
Regarding shooting film - there's a wealth of knowledge and some very helpful people here shooting film still that usually posts in this section of the forums:
Pentax Film SLR Discussion - PentaxForums.com
The GX10 can do some lovely colors when the light is good (not so good a camera in low light, unless you are crazy like me and shoot it with f/1.4 lenses - I have the K10D, the Pentax version of that camera). Regarding the lenses, the 16-45 was always a very well regarded lens and I still think it's super. It doesn't get much love here in the forums anymore because newer lenses like the 18-135 and the 16-85 have a bigger range and are very good lenses as well, but since you already have the 16-45, I would keep it and play with it, I think you will be surprised at the results you can get from it.
You probably have some vintage lenses you are shooting with the P30 (which I also own, in the P30T version - great camera!). You know you can use those with all the digital bodies as well, right? And you can use any modern lens on the film bodies, as long as you use them on one of the automated modes, since they lack the aperture ring. Some lenses, even if they are made for APS-C crop bodies, have a good part of the range that covers the full 24x36 film frame. The 16-45mm, for example, will work very well on your film body from about 22mm to 45mm - giving you a very nice, high quality wide angle lens for your film adventures