I really love Tegami Bachi; I'm glad other people know about it, too. xD
I plan on cosplaying Lag Seeing, and maybe Niche. (I have so many planned cosplays, it may be a while until I can actually get to it. -sweatdrop-
As for the hat? ....Maybe get a large messenger hat that's loose on the top, and cut a hole where his hair falls through and sew a small lining on the rim so it doesn't fray. Something like this
I'm not sure about the bee, though. Maybe get an iron-on bee symbol?? Or stencil it with paint or something.