wezzer

I was in a similar situation to yourself, mortgage young family etc. I did a city & guilds plumbing course and went straight into self employment. It has been two and a half years since i took the plunge and i wont lie the first two years was a real struggle, only now am i finding that i am getting a reasonable amount of work. As for employers, you will find it hard to get work this way... experience and a full plumbing apprenticeship are what they are looking for.
After completing your course i would suggest you continue in your current job if you can and maybe try and put your name about, small adverts in shops, local papers etc and work that you get you could fit in at weekends or evenings until you find you are getting fairly regular work.
Good luck..