Tamiya & Hasegewa both have samarai in 1/35, but not much in "ordinary" folk.
There may be pewter or resin figures of "civilians" to populate such a diorama.
For making the trees, those just beg for the "twisted wire" method.
You start with a bundle of middling stiff wire (bendable but will hold shape after bending). You give that bundle a twist to hold it together up to the first branching, then you peel "out" a wire or wires to create branches from the trunk.
Luke Cowen, among others has some good videos on the technique.
Now, you might have to scour international sites to find white flowers to make the blossoms for the trees if you are keep to capture that classic Japanese painting style set in Spring. You might could get away with some of the railroad products for flowers in fields; but those are going to be much smaller than cherry or magnolia blossoms. But, if the effect makes you happy, then, its all good.
Now, I feel compelled to go see if I can find a video on Japanese Blooming Tree dioramas