Re: Key signature & blues scale
The issue of enharmonic notation only occurs with F#/Gb, which is opposite to C on the circle of fifths. It's not a huge issue.
Reading the blues scale is less important than memorizing the blues scale and how it fits in with harmonic structures. When somebody says 'blues in (whatever key) major" it is actually based on the dominant seventh chord, a type of major-third chord with a flatted seventh. The basic blues scale includes five tones: the root, second, third, fifth, and seventh tones of the scale of the dominant seventh chord. Put another way, it's the dominant seventh chord with a second added.
Twelve bar blues commonly have a dominant seventh chord rooted a fourth (IV) above the key center on the fifth and sixth measures. The seventh of that chord is equivalent to a flatted third above the key center. The turnaround of twelve bar blues commonly goes to a dominant chord rooted on the fifth (V) in the ninth measure and IV in the tenth measure, then back to the root on the eleventh and twelfth.
Your son has two options over the IV chord. He can play the major blues scale over the IV chord or he can play a minor blues scale (flatted third) over the root. In fact, he can add a minor third over any chord, any time he thinks it will sound good. But the fourth above the root of a major third is still a no-no because it tends to clash with a major third. Here's hoping he has fun on the road he's starting with the blues scale.