Hello harrytang,
One thing to do in Japan (if you have not done so already) is to purchase a copy of 天保貨幣カタログ, The Catalog of Japanese Coins and Bank Notes, often referred to simply as "The JNDA Catalog". Learn your coins before making a purchase. They should all have a physical size and weight like those provided on the Numista pages for each coin. Now a few more details.
100 Mon "Tenpōtsūhō"
All official 100 mon coins are of a copper alloy so will not attract a magnet and should look like an old copper coin.
This is an interesting coin because it was often produced without authorization from the government, but these "illegal cast" coins are still valued by collectors, probably because they circulated side by side with the official coins and are a reflection of the economic and political situation of late Edo period Japan.
Nearly all have validation marks, stamped one each on the two long sides. Those without such marks are either bosen (the “mother” coins used to produce the circulation coins, in which case they should be very expensive), fake pieces produced after the Edo period, or an error coin.
1 Shu "Kaei Isshugin"
All isshugin are of a silver alloy so will not attract a magnet, they will have a certain appearance from the silver, steel coins look very different.
There are several variants of the isshugin. You ask about the Kaei variant.
The JNDA Catalog will describe how to distinguish those of the Kaei period. But you also find the main figure from the catalog here on Numista at
N#10811
These are subtle differences in the calligraphy, it may take you a while to learn how to recognize these features. I think if you match the features in the calligraphy, you have a good chance of an authentic Kaei piece because counterfeits will often lack attention to such fine details.
1 Bu "Tenpō Ichibugin"
All ichibugin pieces are a silver alloy so will not attract a magnet.
There are three variants of the ichibugin. You ask about the Tenpō variant.
The Tenpō has three features of importance. If these are present, you have a good chance of an authentic piece because counterfeits will often lack such fine details.
1) The 8th and 9th strokes of the 是 character completely cross.
2) There will be blossoms stamped on the coin sides, 3 on each long side and 2 on each short side.
3) The blossoms on the perimeter of the obverse and reverse faces are arranged such that one or none are upside down. There are specific blossom positions, if any, to be upside down for each of the three variants.
These things are explained in the JNDA Catalog (to be fair, in Japanese, but the figures are quite revealing) but you can also see this described here:
http://charm.ru/coins/jp/Ichibu-gin.htm
Have a safe trip.
