Small altcoin usage effects
Blocks can still be found by miners even if there are no (other) transactions. The reason for this is each block must contain a coinbase transaction, which rewards the miner with 10 coins.

(The above is assuming that your coin is sufficiently similar to something like Bitcoin or Litecoin. An altcoin you create could have completely different rules.)

As for how your mining could affect the economy, well obviously you would be the one ending up holding all the coins. If you're giving them to your friends to then trade, no problem. A few friends is of course not a very large economy.