I'd echo those who have said 'risk no more than 1%'. Money/risk management has to be a central part of one's trading plan, in my view, if one is to succeed in this business.
I would treat it like any other business: draft a detailed plan, covering everything from the nuts and bolts of your approach - including SL placement/management as well as how you identify setups - to some defined rules for your risk management. Psychology is, in my view, a tough aspect of this business, and the tighter your plan the more you coccoon yourself from the worst effects of this. How much exposure to the market are you happy having at any given moment? If having 5% on the table is something you are happy with, at 1% risk that would be five open trades (assuming untrailed SL levels). If you neglect this aspect of your trading plan, in my experience you increase the likelihood of making bad decisions when you hit your first pressure moment.
Say you have five open trades, then spot two five star setups. Your original five positions are all in a small amount of profit, and you had a couple of wins the week before, so you take the other two setups. Then the market bucks, and all seven trades stop out, leaving you 7% down on your account in a matter of minutes. A trading plan will hopefully either help you avoid drawdowns that take you too far out of your comfort zone, or will give you a plotted course out of that. When you take a hit, do you take a day or two off? Reduce risk on the next few trades? If so, by how much? For how long? Or do you just trade through, same risk as ever, because your backtesting/experience tell you that that is the most sensible course of action for your approach? Or any one of a number of other reactions?
This can be a psychological, emotional roller coaster, if you let it. In my view, the surest path to success is simply the mechanical execution of an effective strategy. The more detailed your trading plan, the more mechanical you can keep your trading, generally the more profitable you will be. If you find yourself having an inconsistent reaction to market variables, you will often find that you also have inconsistent trading results.
So with apologies for being preachy, I would start by drafting a detailed trading plan, then make sure that as you start trading you keep it updated. It will become second nature one day, but in the meantime I'd read it pretty regularly.
I'd echo the others who have said that I'd doubt you can support yourself from the proceeds of trading a £20k account, not least because the pressure to make an income would be likely to affect your trading decisions early on. But if you can find an alternative income, ringfence the £20k, then you should be able to trade that up to a size that can throw out a decent income.
I think that it is too easy for experienced traders to make this seem an impossible task to any newer trade, when as you have said we were all beginners once. This is a tough area to get into, trading takes a lot of work at the outset - but then that just makes it like any other career that offers this sort of reward. So I would go for it, but make sure that you have a tight trading plan, keep your trading mechanical and consistent, and don't expect to make a living from your trading right from the get go.
But I can't think of anything else that offers this much financial and lifestyle freedom without the need to work for anyone else and with no surrounding industry infrastructure to satisfy.
I would also add Forex to your trading plan, but that's just me..!
I hope that you found some of this of at least some use. If you make it work you'll be absolutely DELIGHTED with your decision to try trading!
ST