The official data book is a great resource for this kind of information, as it includes information on cumulative distances from the southern and northern terminus, elevation differences, nearby stations, toilets, sources of water, stores and more. If you carry a smartphone with you, you can use Google Maps to get up to date details on what facilities are nearby. You can also visit the satellite facilities and other places like tourism association counters to get more detailed info that locals on the the ground know.

Four Prefectures, 29 municipalities: https://mct-a.org/en/what-is-mcta/town/

You can also get good information about lodging from social media groups.

Facebook 「みちのく潮風トレイルハイカーズコミュニティ」(“Michinoku Coastal Trail Hiker’s Community”)
https://www.facebook.com/groups/2074391539536922

Facebook “Michinoku Coastal Trail”

https://www.facebook.com/groups/michinokucoastaltrail

Note that some outdoor toilets along the MCT route close in some cases during the winter months (December to around March). Also, there are many unmanned train stations along the route, so a train station is not necessarily a guarantee that there will be toilets. Bringing a portable toilet with you is one of the best ways to stay prepared. (Please follow portable toilet instructions and local disposal rules.)