If you have secured your legal copy, here is the workflow an inspector follows:
Even thin-gauge TIG welds are inspected visually. Porosity less than 5% of the weld length is often accepted, but the inspector needs the precise table from the standard. iso 17637 pdf
A: No. ISO does not release their standards for free. However, some national libraries or university engineering departments have viewing access. You can read the "Preview" on the ISO website to see the table of contents and scope. If you have secured your legal copy, here
A: Yes, per Clause 5.2. Direct visual access (eye within 600mm) is preferred. Magnification (2-6x) is allowed for "enhanced visual testing." Borescopes are only required when access is physically impossible. A: No