Installing and activating are normally separate steps: installing downloads the profile, while the clock is usually tied to the line registering with a network or to first data use. The exact condition is written on the page of the plan you bought, so read that one, then install early with the line left off.

Better not to. There is no ground signal in the air, and on descent the phone can register with a network in a country you are passing over or stopping in, which may start the plan before you arrive. Wait until you are on the ground at the destination and phones are allowed on.

No. With the profile already installed at home, switching the line on takes seconds and needs no internet. Wi-Fi only becomes necessary if the profile is not installed yet, which is exactly why that job belongs before departure.

You can, and it is not wasted, because you are using data in a country the plan covers. Before deciding, confirm the layover country is on the plan's list, and check that the remaining validity still covers the days at your actual destination.

Once a plan has started counting it generally cannot be paused, and switching the line off does not stop the clock. What you can do is re-plan around the days that remain, and if there are not enough, buy a top-up and install it while you still have Wi-Fi. If you are unsure of the status of the plan you hold, message us with the order number.