Congratulations on picking up this very rare species!
The trick with them is to thin them down. It's important to keep sunlight going to the inside. I've got one which I should have thinned down earlier this summer. It'll let the fine branching you actually want develop well. You may want to try veneer grafting to get some foliage down lower. There's a pretty good example of the technique
here.
Hinoki is known for taking to this kind of grafting. I was lucky in the ones that I have though. I didn't have to do this to get what I needed. But I can't see why this wouldn't work on a Tsukumo.
The foliage is really fine, so they can dry out pretty quickly. My smaller one is much harder to keep watered properly than my large one.
So pretty much treat it like a hinoki and you'll be good... they just get crazy dense. Slow growers... but you'll blink and realize it's ridiculously dense. lol
Warmly,
Victrinia