Q1-4 Can I check if the land has been approved for development?

You can check it at the Yokohama Building Information Center. In addition, you can view and obtain (charged) the outline (record and land use plan map) using the development registry.
In addition, about contents of development permission itself, as you may be able to obtain a part of book by application based on the regulations about disclosure of information held by Yokohama-shi, please talk with person in charge of permission directly.

Parts to be published in guides on this answer

• About Development Register
  "Guide to Development Permits"-System Edition-Chapter 4

Contact for inquiries regarding this answer

• Development registers and other certificates
  Housing and Architecture Bureau Information Consultation Section Management and Information Section (Yokohama Building Information Center)
• About contents of permission (person in charge of permission)
  Housing and Architecture Bureau Residential Land Examination Department

For specific details in a specific location, please contact the person in charge of each area.