The triggered ability that checks to see if X is 5 or greater refers to the value of X that was chosen as the spell was cast, which may be different from the number of counters it entered with if there are replacement effects involved
Since your deck will be full of instants and sorceries anyway, that prowess ability can grow it into a 4/5, 5/6, or something waaay bigger depending on how many cards you can play in a turn
Sleeves protect cards from wear, dirt, and moisture, and also make shuffling easier
Drawing a card for everyone will typically benefit the empty-handed player more than it will the player with seven cards in hand
If you just want to buy the card as cheaply as possible, you can find damaged copies below $20, though MP copies will cost closer to $40 if damaged doesn't cut it for you
#237 Quick Ball - Trainer Item You can play this card only if you discard another card from your hand