Hi Trent,
It's good to know that you have some experience. It's all doable, it just needs a little engineering. Like the saying goes...all it takes is time and money!
A king post would certainly work, but I might lean more towards a queen post. Then you can use common rafters and support them more mid-span. At 30' wide those rafters will be pretty long, so it will be good to support them. That arrangement might make the venting cupola easier to frame as well. I assume you will put on steel roofing? That will help with snow load, but I would still go 10/12.