How to get arduino to always be connected as /dev/ttyUSB0 and with chmod 0777?
Have you considered not trying to force ttyUSB0 but instead creating a symlink to whatever tty is assigned? Your software then just uses the symlink.
A problem with forcing a particular tty is what if you boot without the Arduino but another device is attached? You then need to convince the other device to skip ttyUSB0.
If you would consider a symlink then something like:
ACTION==&quot;add&quot;, KERNEL==&quot;ttyUSB*&quot;, ATTRS{idVendor}==&quot;1a86&quot;, ATTRS{idProduct}==&quot;7523&quot;, SYMLINK+=&quot;arduino&quot;

might get you started. Check the VID and PID using lsusb or similar. To set permissions as well you can use e.g. MODE=&quot;0777&quot; as you already have.
There is an example at https://wiki.debian.org/udev that might give more background.