The bitcoind 'gen=0' setting - implications?
"gen" is by default 0 (off), so you should not really need to specify "gen=0" anywhere.

"gen" will generate bitcoins (mining), but you should only do this if you know what you are doing (you probably want to mine in a pool, and use proper tuned hardware/software).

And yes, you will only get transaction fees if you mine a block.