there are 2 intensity levels. on the stronger one (which i would recommend) it is definitely enough to hear the call (or the alarm clock), unless you sleep very deeply...

Unfortunately no, you need the Premium APP, but you get many interesting futures with it.

No

Yes, my Göttimeitli is 10 years old and the fitbit fits perfectly!

The 20 sport modes are on the back of the Fitbit app.

Yes, you can. The tracker is waterproof up to 50m. To prevent the touchscreen from triggering in water, there is an extra screen lock mode that should be activated before you start swimming: https://community.fitbit.com/t5/Inspire-2/How-to-use-the-Inspire-2-for-swimming/td-p/4536535

The display can show different watch faces, some of which include the step count. Others show the step count with a single tap on the display. The watch faces can be set in the Fitbit app. You can use your account as before. You can even use both devices (if you wear the Fitbit Flex 2 for a few hours, then the Inspire 2 for a few hours, or both together, the Fitbit app ensures that the data from both devices is synchronised). The Inspire 2 charges in one piece, you can just plug the charger into the back of the watch.

Kann man: https://www.fitbit.com/global/us/products/accessories/inspire2-clip