1. The general opinion I've seen floating around is 500 or so for a minimum.
2. Winrate is generally considered your ROI, or return on investment. This is the percentage of profit you average per SNG. It has almost nothing to do with your "Percent of times finishing in the money" or ITM%. for example:
Lets take 2 people that both played ten 10+1 SNGs, where the payouts are 45 for first, 27 for second and 18 for third.
Person one has 3 firsts and 7 losses. The ITM is only 30%, but they have a profit of $25
Person two has 6 thirds. Their ITM is 60% !!! . but they LOST $2
yourself to see your ROI.
3. The larger the field that starts, the larger the variance so you'll want a smaller % of your BR being used the larger the fields get. 2% is for the big MTT's
4. The swings. I seriously doubt that a quality SNG player would have swings of $40 up and down at the $2 games. I mean a swing of $40 is like losing 19 SNGs straight. Highly unlikely.