The resolution of the photos should be at least 1200 px wide x 800 px high (72 DPI).
Yes You can select multiple files using the Shift or Control keys (Shift / Ctrl). You can also upload additional files by clicking the "BROWSE FILES" button again.
Yes, of course, the files can also be sent as ZIP.
You can change your photos, your video and / or your logo up to a maximum of 3 times a year if they are no longer up-to-date.