Build a strategy before you papertrade.
Building a strategy requires historical analysis (backtest) of the drivers of returns in your strategy. For example, if your plan is to buy stocks that have been rising in the past 5 days, how well has this strategy done in the past 20 years? What are the drawdowns and risks? How correlated is this to SPX?
You will want to stitch together a strategy and backtest, define risk limits, etc., before you try to paper trade. Frankly. once I have a strategy that has been backtested (robustly, so make sure you are adjusting for data errors and sampling bias!), I start allocating capital in small amounts, e.g. 5%. As I gain more confidence and a track record of performance for the signals and strategy, I add more capital. I'd say my trading strategy has signals that decay and are replaced 1-3x a year.