I second the anon above. I think in general you're really great at handling his maturity, but lately it seems that his seriousness has been outweighing the fact that he's a fluffy dork who's actually a big sweetheart. I think you should play off that idea more. Have him be more protective of the people he cares about, have him be more flustered by things that would fluster him (as opposed to have him be like "B| no gfto").
I think you're doing a great job with tagging around with Kohaku. I think it'll be even more noticeable once you're a bit more consistent with your activity, as you said already. You tag around a lot, though it may take longer for you to come back to keep tagging. But at least you're putting in the effort; just keep trying!
I do think that, sometimes, Kohaku comes across as a bit flat. I'm not sure how to describe it, but his responses can be a little generic and hard to respond to (unless you're Koryuu, I guess). I think that, clumsy as he is, he's still an angel and it'd be interesting to see that side of him come out a little more, either with interactions with the birds or singing etc. It'd also be great to see him wanting to help people, too (kind of like he wanted to with Shuichirou in canon). I think you do a good job capturing his flaily/clumsy and silly side, but there are definitely other sides to him, too, that'd be fun to see explored more.