The one thing I would maybe re-think is if you should base your long-term objective on a compounding profile versus an income profile. We all start out with some figure, compounded to infinity in mind. But ceilings get hit pretty fast, so be careful there. If you don't think a measly 10 contracts has any impact on short-term movement in a market like GBP futures, think again.
On further thought, I think people are being a little casual in figuring out how much would really be required, myself included. It's really tough to start right off the bat depending on your weekly results in order to keep the lights on and put food on the table, so it's good that you have a bit of cushion already for living expenses. But frankly, I think one really shouldn't go full time trading unless their monthly expenses are just a fraction of what they expect to earn trading -- as if almost an afterthought. So don't even think about how much you need to take out of the market right now to pay rent, think of your 10K of savings as your expense account right now and just trade to trade (this is assuming you have 10K apart from your trading account).
To give a personal example, after spending years of "re-learning" how to trade, I've put all but 5K of my trading capital in a savings account. With the 5K, I am back to trading a single currency contract on an intraday basis, and all I expect myself to do for now is to earn ticks, not dollars, day in and day out. Is 5k all that is needed to make a living? Perhaps for me from here on out, but not if you count the hundreds of thousands I gave back to the market in tuition over the years. So for me, percentage return means absolutely zilch; this 5K I'm trading with also doesn't really mean much as some absolute figure to start with. Just so you know where I'm coming from.
Good luck!
