You have to make sure that the keyboard language is set to German. I held down the # key in Whatsapp for about 2 seconds. Then simply press the number 2 4x for e.g. Ä.
No, unfortunately. However, without Whatsapp there is no need to activate data and the battery lasts indefinitely. With an unlimited SMS subscription, this is also fine.
Grüezi, under the setting "Accessibility" you can set "large font". If you like, I can measure the font in mm as soon as I have access to the mobile phone (it belongs to my papps). LG, Anita