I work in this industry, unless you already have a solid capital to put down then this short selling is not for you.
If you buy a trade in the evening based on predicted positive annual reports being release the next day first in the morning or a new product launch being received positively, the stock might jump by 5% so if you pumped in £200,000 you've just made £10,000.
Now with smaller amounts such as $1000 bucks, the trade will swallow up around 10$ in fees, the you have the difference in the buy-sell spread, the value of actual shares hitting your account will be around 970$ by then or so. The shares go up by 5%...that will redeem you to $1018.50, sell this and another fee is whcked on for 10$ bucks and you're back to $1008.
5% is a very good return on a single day.
Smalled cap is more volatile, companies can jump up by 20/50% in one positive annoucement, but they also tend to drop very hard. Smaller cap investing to me is closer to gambling on horses IMHO. Unless you do your research and invest in healthy businesses for the medium to long term.
I can go on rambling.