G Coin clarification

G Coins are an in game source of money as you recharge for G Coins, so my question is this

1. Can you use them to buy packs in the direct shop, example hero/angel packs.
2. Is there a limit to how many times you use your coins a day, example you can recharge on your CC 5x a day so is it the same when using G Coins, you can only use them 5x a day? or is the use of them on items unlimited as long as you have the coin.so in other words if i recharged 30k G coin could i buy an item 20x or would i be limited to 5 like a normal buy with a credit card.
3. Am I correct in saying you can use your G Coins to purchase diamonds?
4. What is the overall limitation of G Coins.
5. Does anyone even use G Coin?