As for the collecting side, unfortunately right now buying boxes rarely has a good financial return as only 1-2 cards per set are really valuable and even if you hit an enchanted it might barely pay the box back depending on which one. So collect what you like and do it for the love not the money

Exciting! Playing definitely the starter decks. Good way to get a deck and learn the basics. I would check to see if a local store to you has a weekly league you can start participating in and start learning some of the strategies from the locals