Toranaga is Ieysu Tokogawa, the setting is the late sengoku period
Id go back slightly further than when shogun is set but not at the start of sengoku, just go to a guy called oda nobunaga, he's the first big character, hideoshi toyotomi being the second (he's the old guy who died leaving the young emperor in shogun) then Tokogawa, those 3 between them unified japan
Edit - and hoping that shogun is a big global success the next one that needs the big budget TV show is romance of the three kingdoms, a semi fictional book from the han dynasty period in China (dynasty warriors if you know it - and to be fair a bit of my Japanese history comes from samurai warriors) that's got more content to cover, would be like a Chinese game of thrones, there's already been some films on it like red cliff