I appreciate the enthusiasm you are showing... but the horn is NOT a shortcut to an end result. You can't buy a piccolo trumpet and play lead in the jazz band.
You can't buy a C trumpet to get a whole step higher range. You can't swap from an 8335 to an 8310 and suddenly be a completely different beast.
You have the chops or you don't. Jon Faddis will sound like Jon Faddis even on a Conn Director cornet with a 7C mpc.
A lead player does want a suitable horn to fit their playing style, but not all lead players have the same style so there is no ONE recommendation for the perfect lead horn. Some like large bore lightweights. Some like step bore horns like the Shew you mentioned. Others like huge bells and loose slotting ... get it??
Some jazz players like big dark horns like Botti (and legions of others like Chet Baker et al). Some guys like a brighter sound and more resistance to push against. Each has a different sound.
I'd say that a flugelhorn would be a better buy than a second Bb for jazz solo purposes if you do not already have one.
Unless your kid is seriously pursuing an orchestral path I don't imagine he will be getting much use from a C trumpet. If he IS considering that path he needs to be studying with a like minded pro teacher and beginning to practice playing Bb parts on C (and D parts on C) and also working on transposition books like the Sasche. also starting to tear through the Sachs Exercpts book... and Charlier!