Yes, international data is supposed to be a flat charge (same as domestic, $10/GB) and international calling happens at what I would consider to be very reasonable rates, both to numbers in and from towers of foreign countries. Also, I believe there is unlimited international texting around the globe.

(I migrated from Verizon to Project Fi, and live close to Canada, so, consider that I am used to turning my phone off when out of the country or near the border, because of Verizon's very unreasonable rates for international calling and text.)

I don't think you can order a Project Fi account as a non-domestic resident, though.

Yes, and at the same cost per gig as domestic data.

See Fi's rate card here: https://fi.google.com/about/rates/