Canon EF 8–15 mm f / 4L Fisheye USM - ideal lens for panorama photography. With an appropriate adapter (like nodal ninja) at 12mm for a full frame camera, it takes only 4 photos to stitch a full 360 panorama. With a Canon 5Ds you will get a equirect with 18x9Mpx.
The order is as follows: 1) upload to the site spherical panoramas from which you plan to create a virtual tour; 2) from the list of uploaded panoramas add each panorama to the virtual tour (Add to 3D tour link); 3) open the created virtual tour, edit the panorama order, select the main panorama, set transition points (tunnels).