I'm not helpful at all but I have a handful of spirits from that listing. Yes, they usually confirm that they were bound. There is no further information, since they are 'famous'. Well, if your spirit is not as 'famous' as Elvis, then you'll have a problem with offerings. The biography will usually contain favorite scent and colour. You can also ask specific questions via the order notes.

I wouldn't claim any special knowledge of the right way to bond and honour him, beyond the standard tips in the forum.

I think reading that book will help you get to know him. I've read people say here that looking into the history of a period can help to get a feel for the times the spirit lived in. Maybe read both his books too, including the second less well known one? I think he may have given life advice in that one, which I've not read.

Maybe check out YouTube videos on his style of swordmanship? His school is mentioned in his Wikipedia entry.

Learn za zen (Zen buddhist sitting meditation), like he did? Just a few thoughts.

I really got into some aspects of Japanese culture when I studied Aikido, that related to the philosophy of that martial art (Ki etc). One of my Aikido teachers taught us za zen one weekend. It's a good insight into 'being in the zone', as they call it nowadays, which I think that spirit really was.

As Lewk suggested, learning Zen meditation is not a bad idea. He was known to consult with Takuan frequently. And yep, get books, novels, movies, even mangas about him and people around him. There are some about Kojiro and Takuan as well.

About kendo and stuff, not sure, ask him about that. I'd guess if he is reborn in this day and age with the same personality and potential, he'd be into more brutal and competitive sports rather than kendo : p