No limit,
I would recommend My-track for a US account, they have, hands down, the best real time trading tools on the net IMO.
Now, if you plan on trading for yourself, you must read, read and read, do not jump into this thinking you will will make fast easy money. Guys like myself live off of people who do this, it is a one way ticket to broke ville.
I will take a little time this week and post a message with some good do's and dont's for you, I will try and do it before the weekend.