If I apply online for card and get approved anyway to use it right away for free luggage and 10% point rebate?
Re 10% rebate; you will get it as long you have the card when you fly, regardless of when award was booked.
Re free luggage; my experience was that within hours (maybe minutes?) of getting approved for the card, my upcoming itinerary (booked months earlier) started showing free bags for everyone on my reservation.
To make things complicated (sorry), I had 6 people on my itinerary, 3 of them minors, and we all had free luggage; though according to the card's benefits terms, it's only supposed to cover for card-holder + 3 companions.
Maybe the minors aren't included in the companion limit?
Maybe because at the time I booked, I was Mosaic?