Regarding litterature, the idea has been brewing since I studied japanese history some years ago at university, and since then I've been living in Japan for half a year, and I'm going back there this autumn. Seeing castles and armours in museums is a good inspiration, even though Osprey's books works just as well!

Being interested in Takeda, have you checked their book on Kawanakajima? It's quite nice.
Regarding colour scheme, I'm really torn between a "realistic" samurai army and a "table top" army with a proper colour scheme. The first one would probably be much less cohesive, but it would allow myself to put many of the generals from Sekigahara on the table, since Perry miniatures have several of them made. However, it would be more of an explosion of colour like Bretonnia, and I have yet to see if it works out well, since I'm still on my first samurai, trying to figure out whether black primer (my usual method) it better than white primer for them, since I'm having a hard time getting all the details to show. Those Perry
do are so tricky to paint! The ashigaru will probably be easier, as they will allow me to paint them in uniform colour, either I'll go with only ashigaru from one general for a complete uniform look (all red, like Mephistofeles, looks great), or I'll make them from several attending lords. Hopefully the flags will make it more coherent, but I'm slightly afraid that they will end up like a big blob of paint from a distance. *sigh*