...So do I just pull whatever I have listed and add it to my starting pack?
Yes. You've already done the legwork of determining if your attunement limit allows you to equip the item.
As such in a 2 player game I’m allowed to replace any cards in my beginner pack with any X gold cost cards. So essentially I can replace all my basic cards with upgraded ones as long as the adventure is lvl 2 or higher then begin our game?
Wrong. Reread page 26-27 about replacing a card or cards that add up to the cost. It might be possible to mistake the "card(s)" in that table to imply all cards in that persons equipment pack, but it is much fewer cards.
The reason they list the (s) is for splitting it to multiple cards per character when the cost gets to 4 or more (2 + 2 = 4, so 2 cost 2 cards are possible) and to include multiple characters. As stated, in a 2 player game both characters would have 2 classes, so both would get this option. In a 3 player game only 1 character would have 2 classes so only that character could replace 1 or more basic cards with Market cards.