Your following setting to feed rbfeeder from Flightaware's dump978-fa are perfect:
[dump978]
dump978_enabled=true
dump978_port=30979
The memory problem is caused because you have both tbe dump978-fa & dump978-rb installed and running.
Since the dongle is grabbed by Flightaware's dump978-fa, the RB24's dum978-rb runs dongle-less, and keeps restarting continously, causing excessive use of cpu and memory.
To solve this problem, uninstall RB24's dump978-rb, and reboot the Pi
Note: Do NOT change above noted settings in file/etc/rbfeeder.ini
sudo apt purge dump978-rb
sudo reboot