my advice to a 20 year younger self would be, digest / consume all the free information you can before dropping any coin on books or videos etc. these days there is so much free info out there, you just have to look, two words for you: Forums, Forums. Find a specific forum for you vehicle, or for your engine, or jump on the HP Tuners forum, cover yourself up in some thick skin, as some guys are jerks, and ask a bunch of specific questions, filter out all the BS and build away.
I have not used the tuning school materials so I can't recommend them.
I would suggest you consume as many YouTube videos as you can, but don't watch 12 hours worth in one day, watch an hour every other day, know what I'm saying, let your brain rest.
Here are some smart dudes that I enjoy watching. Oh, just because a video is not exactly about what you need, watch it anyway it may give you the foundation you need to build on, then you will find they all have 70% the same content, but it's that last 30% where you find the gold nuggets.
Yes I've watched some of these videos and barely understood 10% the first time, that's ok, there is a lot of information, so grab a cold one and watch them a few times, it's all good we all learn at different speeds, I applaud you for taking this on rather than [ahem] gaming, ha ha
In closing you will find a lot more dudes are doing write ups on what you are doing than what I am teaching, because everyone wants to run before they can walk, ha ha.
Mega Mechatronics
Engine Tuning 101 - Part 1 - Intro, Lambda, Wideband