Seating is still unknown, but tickets are already on sale at sites like ticket.co.jp
Some of the Hokkaido ones are going for under 30000 yen, which comparatively cheaper than the Tokyo tickets that start from 60000 yen. xD
Nagoya Dome results will be released in the beginning of October.
*crosses her fingers* (>_<)
[Edit: please read this guide first before asking anything related to buying tickets]