how bad is this ?

Agree with StephenB​ that the log entries are not a critical concern.  Any time a router is exposed to the internet, it will receive all sorts of connection attempts (just as our phones and mailboxes receive unwanted attention).  The router firewall simply ignores all of these attempts.  Netgear includes software which records these attempts and tries to make sense of them using algorithms (which are not documented anywhere) and the results are posted in the log.  One interesting note is that Fraggle Attacks most likely originated within the ISP network, which indicates that one of their other customers may have been hacked.  (read some internet search descriptions of Fraggle Attack.  Fascinating.)

While not a high end product, the RAX50 should have no trouble supporting 25 WiFi devices.  Investigating that would be a more productive use of time & effort.