Questions about 365 Family

You can enter up to three licence codes, for each one entered the term is then extended by one year. Or enter a code every 364th day. If you do not do this, the subscription expires and the functionality of the software is restricted.

I use English as the display language as well as the proofing language. Thus: Yes

Effectively only the delivery method.

Retail = Delivery of the licence key with packaging and dispatch via post.
Download = Delivery of the licence key via email or user account.

However, both versions must be downloaded for installation.

Here is the official answer from Digitec, it was a bit buried, so for once I am not angry with you:
www.digitec.ch/de/s1/QuestionAndAnswer/was-ist-der-unterschi...