Just found this thread and wanted to add something from my own limited experience. There's a lot of folks that seem to have a lot more so take it for what it's worth.
I come from a knockdown karate background and also train in Judo, hence why Kudo was so interesting for me. From my own experience and from what was actually told to me, if you want to compete in Kudo you're actually better off training at an MMA gym and once a week getting together with like-minded individuals and training under Kudo rules. The reason being, Kudo now has grown far beyond its beginnings and those two aren't going to give you all you need to succeed.
From what was told to me, rank in Kudo is performance-based so you need to be fighting competitively - in Japan and Russia, fighting in Kudo tournaments may be easy but here in the States not so much so picking up smokers or competing in Judo/BJJ tournaments would be the way to go.
If I had the opportunity, I'd train in Muay Thai and Judo and once a week get together and mix it up with other guys who want to fight under Kudo rules.