I don't think there's a simple answer. A better than 50% win rate is good but if your money management isn't tight and you incur large losses, you won't get anywhere fast.
Up 35% in 3 months is very good but it may be nothing more than the good fortune of a finite sample in a cooperative market. Or not. Time will tell.
When to increase size is a personal thing as you have to balance results with risk. In early '07 I began experimenting with a pairs trading system on somewhat illiquid stocks that looked good on paper (the hindsight of backtesting). I began trading it with several 400-600 share positions (200-300 on each side, long and short). As they worked and as I discovered add'l nuances that only come from real time, I began slowly bumping up size, more so as profits were booked (substituting legs to book profits, shifting bias intraday, etc.).
I believe that when something is working well, you keep hammering at it, increasing size the longer it works but never more thanone can eat when it doesn't. It's usually the last trade that gets you
but by then you should be well ahead and one trade isn't a killer - it just becomes the cost of doing business. At one point in 2010 I held nearly mid 6 figures of pairs inventory but by then, the strategy was on the decline. Edges come and go and eventually, so did this one.I'm not confusing brains with a raging bear market. Trading in a GFC was a lot wind in the sails and the edge is gone. Or maybe not an edge, just a being in the right place at the right time. Call it what you want.
The short answer? You have to scale up within your comnfort zone, make hay while the sun shines and at all times, practice good money management so that nothing ever hammers you.