The standard of living is far higher in the US plus it is a lot easier to get back to the UK to see friends and family.
In answer to the original question, NO you can not get a visa if you are self employed unless you have over $1 million cash invested.
Big losses? You should never expect or tolerate big losses. Protecting your equity is the main skill you have to learn. Use a risk/reward system with a ration of 1:3. Enter several positions a day and you might have losing days but they should never be crippling losses.