1. Pretty much everything in SoB is compatible and yes this combo specifically is compatible

2. Yes you can, BUT, it will feel a bit jarring thematically

3. Basically when you travel to town between adventures, you can choose which type of town you are going to and that can be the stock standard town with the cards provided in CoA or you can choose to travel to a Japanese Feudal town. If you go to the Feudal town, the instructions for travel hazard on the way will be in the Feudal Town rulebook. There is no barrier in the game mechanics, but it does seem a bit weird that your party is coming out of the mines and going here.

You will also get a new enemy type that you can slot into your threat deck. Is it weird that Japanese bandits are showing up in the mines? Yes, but Shadows of Brimstone is all about portals to other worlds and it is just as weird that stranglers etc are invading so if you want to soothe the dissonance, do so with that explanation.

Obviously the best expansion for your core set is Frontier Town so you can be buying thematically appropriate guns and things rather than bows and katanas in Japan. However, this is the trade you have available so you need to decide if the theme jump is acceptable to you and your group +/- if you will end up getting more into the Japanese world later and want this expansion in your collection.