Q1-4 Can I find out if the land has a development permit?

You can find it at Yokohama Architecture Information Center. In addition, you can view and obtain (pay) 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 acquire a part of book by application based on the regulations about disclosure of information which Yokohama-shi holds, please talk with person in charge of permission directly.

References to this answer

• About Development Directory
  "Guide to Development Permits"-System EditionCHAPTER 4

Contact for inquiries regarding this answer

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

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