first - be careful when shorting, make sure you have stops in place, etc.
short on IB - click on stock, click sell, it's done.
if it's RED, you can't short.
if it's GREEN, you can.
if it's a fuzzy green/black, it's not, but they may be able to get shares.
if you're above 25k, there's no limit for number of stocks, as long as you don't break margin limits. see PDT rule for what the margins are and on under $5 stocks, you have to put up between 2.50 and 5.00 margin / share.
