these are pretty simple questions that bitshares documentation can answer
1 - about the peg, read about black swan and global settlement
2 - openledger is just a gateway for bitshares, same as rudex, criptobridge, etc . What this means is, its basically the same exchange, just a different ui and a gateway to withdraw non native assets (steem, eth, btc...)
3 - the withdraw fee (non native assets) is set by the gateways, not bitshares. Not sure if i understand this one, as the fee isnt very different from other exchanges