The base set alone is 105 unique cards, numbered 001/101 through the secret rares
Prices are primarily driven by the Full Art and Secret Rare variants , which were produced in lower quantities and are increasingly difficult to find in top condition
These go on the Stack at the same time, and you can choose what order they go in - but each effect is identical, so it really doesn't matter
Short answer: Yes, Japan Showcase cards are valuable, especially fracture foils
If you want to cast Boulder Jockey, you'll have to pay three mana plus give up one of your land drops for the turn
The first time you crew it each time, you can draw two cards if it was double crewed and you smash face, I really like in in Zombie token decks since they have loads of spare 2/2 tokens running around to double crew it