Check out John Cornell
http://storagetanks.info/index.htmlHe does a lot of on line training and puts on a lot of classes and training.
And all he does is tanks. No PV or piping.
And you are more than welcome to what I know and can help you with.
The study guides are good, but the bulk of the questions will come out of 653, 575, and Section IX. Know 651 and 652,
Section IX stresses WPS, PQR and WPQ. The big part of the open book is having your documents tabbed where you can move around in it.
You are making a good move. There have been more tanks built in the last 10 years than were built in the previous 25. I call that job security.
Get the TES certification where you can be there from putting in the skillet to blind it off to pulling the skillet to put the tank back in service.