I like that page! In Japan, cancels are collected and premiums small to large can be expected on these issues - not so much on this side of the Pacific.
The second group you show are called kobans, nicknamed for the earlier oval coins and the oval shape of the lower value stamps. All 3 are genuine, of course.
The roman letter cancels were used for foreign mail. If originating from a small town, this would be struck as a transit mark on a cover or card.
The second has a large Bota killer cancel, (I think) from Niigata and reversed from what is usually found. See also:
http://www.sanrizuka.com/koban/Bota-Collection.htmhttp://www.sanrizuka.com/koban/koban.htmThe third is a generic telegraph cancel on the 15 sen, a value often used to pay telegraph charges.
If you like, let's see the other Cherry Blossoms (1st, 5th and 6th stamps from left, top row). The left 20 sen looks forged, the other might be genuine.
The 1 sen in the top row is one I've seen but can't identify. The 4 sen in the top row has a postage due cancel. The 2 sen in the third row has a small Bota cancel, "O" for Osaka.
The souvenir sheet is a non-postal item produced by the Japanese post office. There are around ten different showing the earliest issues. While relatively accurate, the originals all vary from stamp to stamp so they can't be used for comparison purposes. To be absolutely positively sure of ID, stamps have to be plated. More here and found elsewhere here on SCF:
https://goscf.com/t/70117Still, they're nice to have when we can't afford to get all the earlies (like me).