Ok - thanks a lot for the support!
I summarize again to make sure I understood everything correctly:
- The settings under “LoRa - LoRa” (keep alive, frequency plan, static GPS…) are exclusively for semtech UDP.
- Basic station has no “keep alive” status data.
- The gateway shows only the uplink data of the nodes in the TTN live data overview if the basic station mode is used.
- The frequency plan is fetched from the TTN settings and not set on the gateway when basic station is used.
Is this all correct?
If yes - then I finally understood how it works 
Thanks a lot!!!