1. You first need to set the current OS to GameOS before you can boot into safe mode, you should have the option in your Red Ribbon power menu iirc.
There is also a shell script you can execute from the command line, it's available on psdevwiki or in github repos.
2. You only see USB storage because you did not set up your internal hdd for Linux usage, that requires installing a specifically patched PUP update in order to create a smaller hdd partition for GameOS so that the blank space left can be dedicated to OtherOS later, this needs done prior to booting petitboot & the Red Ribbon Linux DVD installation.
3. You may need to review the wpa configuration to get WiFi to work.
Also iirc, depending on the PS3 model you are using, there could be some issue due to ethernet & wifi both sharing the same mac address, you may wanna double check that too.