Yes, it is accepted to ensure a visiting pilot has the rating corresponding to the pilot skill standard set by the Japan Hang & Paragliding Federation (JHF). IPPI 4 corresponds to JHF Pilot and IPPI 5 to JHF Cross Country Pilot.
There is no legal requirement for minimum insurance coverage, but JHF requires all pilots to become a member of JHF, with which they will be provided third party liability insurance coverage.
JHF recommends all pilots join its group insurance contract which covers medical and rescue expenses.
See above.