it´s been a while since you first posted and most states are opening up, so I guess you guys have taken some steps already, but just wanted to say a couple of things from my perspective. I think you should just wait and let your son make the decision that he sees more fit to his case, only he will know whether he´s trans, a CD or God knows what he decides; the best help you can give is to give him room and support, let him explore and find his own way.
He probably found this already, but you can always point out that there are communities where he can exchange ideas, either online, or hopefully in person, school, community support groups (depending on where you live) of course therapists are a great help.
As for dressing, how about just wearing (little by little at first if he's not ready yet) androginous clothing? I dressed almost full time for a while and at first I wore clothing that was kinda ambiguous, nice cut pants, silly t shirts, even when I was a teen I sized some of my sister's trousers so they'd fit me and wore her clogs out, again, kinda ambiguous, I knew they were feminine but the other kids just thought I was being weird.
One thing you need to make him be very aware though, he's still a child, without much experience in the real world, specially online, is not always safe out there, emphasize to him that just as much as he's trusting you with his dressing he needs to be aware that he needs to protect himself and trust your guidance when it comes to this new people he's gonna find