Paper trade as long as you can...at first its all about education and getting comfortable, no point in losing $ before you understand the strategy....when you do start with real money, just take small positions of 100, 200 shares to get comfortable...no specific profit goals, just your understanding of risks and rewards

I think there is no general answer to how long one should paper trade before trading with live cash. I personally believe in the baptism by fire approach with a (very) small position size because if there is no real money on the line you will not feel the same emotions as when you are paper trading. As to the minimum account size: Tim suggests a minimum of $3k as far as I remember and I personally think thats a reasonable minimum. One very important advice in my opinion is that you only should trade with money that you can afford to loose. Trading with "scared" money will lead to bad emotions which will lead to you blowing up your account.

Agree with Tim. Learn it first. Paper. Take as long as you need (varies) to really understand how to trade the setups you like, and only trade those that you know well when actually playing with live funds. Use a balance of hopefully no less than 10k. Then trade small lots from 100, 200 shares to test and apply real transactions with little capital at stake, but real emotions, sorta. Later use real money and more profit oriented lot sizes, but make sure you do not use too much of your total stake on any one trade. Do not set profit goals, because that leads to artificial forced trades, and paper or real, that is a no-no. You can only take what the market gives you, no more but hopefully no less...

I agree with Nifri, Tim and Big_T. I'll just add that another benefit of paper trading, aside from getting familiar with setups, is just getting used to the software and knowing it inside and out. Being able to navigate your software fluidly and quickly makes things a lot more comfortable imo.