yeah the japanese overworld spots for the japanese stuff are found in the in the MV Trinity World Tileset Bs prefaced with the letters C and W. If you check yourself on one of these tiles sets (or the tileset in the Samurai RPG for VX) you'll notice an EVIL japanese castle. That is more important than the snow japanese castle because I can warp the players inside where I can't for the snow japanese town. Also within the MV trinity tiles Is a steampunk city, a White Arabian Castle, a dark church, and a mess of giant thorn vine which I guess people could walk on, get hurt by small thorns, and are blocked by thorns that are too long. It could be a business investment to buy the MV Trinity DLC and see them all for yourself. Doing world map areas would be good since many people would want them do to matching the world map area they are planning on doing (having done the world map or have looked through the world map tiles). There are multiple special Steampunk locations. From the normal Tileset of both MV and MZ is the Volcano, however, you told me you have plans. You have sites marked on your world map including a giant crystal cave you could do... All World Map locations are worth it in my opinion.
Lots of good ideas here...I'll take a closer look at the Trinity set and see. Steampunk's been on our list for a long time and I really need to get that one finished. Actually the thorn area sounds fun as well.