I don't know if you put any time into practicing to serve to incorporate this big change into your serve or not. Sounds like you didn't because you said you got 10 double faults in your final set when you made the change.
It's not something you just change without spending enough time in practice to get used to the adjustment. This is a huge adjustment in my opinion, so you need to take a basket of balls out to the court and spend enough time practicing your serve only to incorporate the change into your serve.
I can tell you that changing from the eastern forehand to continental grip on your serve will change the entire dynamic of your serve. It's not going to be a simple redirection of anything that you can simply adjust on the fly on your next match without any practicing.
On your question of pronation, the whole point of the continental grip is to force pronation to happen naturally. If you're doing everything right, you don't need to learn to develop pronation. But you'll need to learn to adjust other things like your timing and stance and direction to get it right.