The best thing to do is to contact our customer service directly. Our product experts will be happy to check the situation in more detail. You can find the contact details on the following link: https://helpcenter.digitec.ch/hc/de/requests/new
Theoretically, it is probably possible, but I have not tried it. It is most likely too cumbersome and would already fail for email accounts with two-step authentication. The Cat B35 is good for telephony and texting, the battery lasts almost a week.
I haven't tried that, but I can't imagine that it would work. That would be apps based on Android. But Cat B35 works with Kaios, its own operating system.
If you use two SIM cards, the first supports 4G, 3G and 2G. The second, however, only supports 2G. You can permanently deactivate mobile data:
Settings - Network & Connections - Mobile Network & Data - Data Connection - Off