Hi guys. A little background first. I'm finance PhD student and have developed a rather profitable trading rule using intraday data. The rule is very robust in predicting close to open movements in stocks that fit certain criteria. I'm thinking of starting an LLC with a seed capital of around 50-100 grand to see if/how well it works in reality. Although I have a lot of education, I have to honestly admit I have no experience trading. What tools would you recommend? The rule was based on average quotes posted within 5-10 minute intervals when trades are to be executed - hence, it presupposed that if a market order is placed some time within those intervals, those would be the average prices I'd have to pay or would receive on a sell. I reallize the danger of market orders (although it is directly incorporated into the rule and it is still profitable) and am considering switching to limits instead. Commision difference is no big deal. From your experience, if I place a, say, limit buy, and the price declines below the limit, how likely am I to get screwed and get it filled at the limit price and not at the prevailing market price that would be lower? If it works the way it seems to on paper, I'll be trading around 4000-5000 per trade. What tools would you recommend? I don't want to pay a per share cost, given the volumes involved. I was thinking of starting out with Ameritrade and then maybe switching to direct access. Also, what is your experience as far as afterhours trading is concerned (big cap big volume stocks)? Thanks a bunch in advance.