I would keep it in a pot big enough for room to grow, let an escape branch or 2 or 3 get to 3 or more feet long, you need to thicken the lower part of the trunk before moving it to a small bonsai pot. You can even use the pot it is currently in, just repot to change the soil to good bonsai media.
Biggest mistake I've repeated over and over is not taking the time to thicken trunks BEFORE moving trees to nonsai pots.
With hinoki, they will not back bud once wood has developed bark. Keep branches you need for final design pruned very short, to keep foliage close to trunk. Do this while letting the 2 or so escape branches extend. Hinoki's in time tend to graduate from mame to shohin to kifu to chuchin to omono, and so on. Reason, foliage keeps getting further and further from trunk. No choice but to let the tree grow bigger to get proportions right. But if you keep foliage close to trunk, with the plan to let it become branches later, then you can keep you hinoki in scale for the long term.
Nice tree, I like it.
