If yes, which pins from ODrive should I use?
Depends, which Arduino and is anything else connected to it?
I have an Arduino Mega, which has attached an accelerometer sensor (<1mA) and a Wifi module (<14mA).
I’d definitely say that’s fine – just make sure to not draw more than 100-200mA or accidentally cause a ground loop.
From which ODrive pin should I take the current for Arduino?
AVCC pin?
Does it give 7.5V? I understood that this is the minimum for the VIN pin of A. Mega.
VCC from the ODrive is 5V. You can power the Mega with it as long as you connect it to the Mega 5V pins and don’t connect the VIN power as well. You may want to cut the +V cable in your USB cord to avoid backpowering the connected computer when programming/debugging.