If it's not cranking at all, could well be the ignition switch.
But check all the earths around the battery and connection to the engine, make sure nothing is loose.
As for OBD readers, I have a cheap, bluetooth based one that connects to my phone.
I keep that in the car for on the fly diagnostics and have VAG COM on the laptop at home for in depth.
The basic ones are good for giving codes and pointing you in the right direction.
For the price, you can't really go wrong.