Issue #1. Simply put, you don't get to choose your flipped item. It will randomly be one of the three it shows you. It's like a dice-roll with a "3-sided die". You've got a 33% chance of getting the item you desire. If you didn't get what you want, you can pay 30 gold for a 50% chance of the leftover two. If you still don't get the item you want, you can pay 90 gold to automatically get it. EA makes games for profit. Basically, like most "free-to-play" game makers, they prey on your impatience. If you are willing to wait, you'll eventually get what you want. If you want it sooner, start buying some gold packs.
Issue #2. The items you have in your stash are GREY ITEMS. They can't be installed on a part that requires GREEN ITEMS. You need to farm the correct amount of the GREEN ITEMS and you can then install them. Same with BLUE ITEMS, etc. Sometimes you can find these in the Black Market to purchase (with gold or winning$), or sometime they are divvied out with the 5 free daily Loading Dock crates. Optionally you can buy crates (5 crates for $20,000 winning$)