I agree w/the previous poster
Take those Wilton lessons. Hopefully you will get a really good instructor and learn much - well the basics
Yes, wait for the class to buy. I've been away from teaching and decorating for so long now I don't remember what is in the Ultimate Decorating Set so can't advise if there is unnecessary stuff. Just know that the instructor is there to *sell!* 1st and teach 2nd so there will be things recommended that one can do w/o by improvising w/things one already has on hand at home.
I was (well, still am) very much a book person. I still have a few books. When I started in this the internet was not available so I never really got into using YouTube etc much. Also, I find having books gives you better access and pictures; often good instructions etc. Trying to learn from books didn't do it for me, until after I had taken the Wilton lessons. Most of what was in the books just confussed me until I had learned the basics. & I have heard of people who had learned on their own who were doing things backwards & such. Having someone show you how to do it right from the start is much better than hav ing to UNlearning what you taught yourself wrongly.