Yep I do understand this but I get rang up a lot to do domestic jobs where other sparks have messed people about and been unreliable. It's seems people are willing to pay decent money for a reliable and competent spark.
I only do domestic work, and get a small amount of work from local advertising etc, but probably not enough to survive on (not knowing your personal circumstances). My main income is from word of mouth advertising and big chunk from other trades, builders, kitchens & bathroom fitters.
So to concentrate in one field, starting up for yourself, might be problematic. Subbying for others, might put you in good stead early on, before you build up your own business.
Good advice from the other guys about domestic work, people want to skin a fart nowadays. 'I'll buy all the materials from Screwfix/B&Q, if you just provide the labour', is a phrase I often hear. So finding a niche in the commercial/industrial field, might make life easier.
I read here how others have kept a day time job, as well as being self employed, building up a business. Difficult balancing act I would expect.
That said, having worked for various employers, very much like being self employed sole trader (apart from talking to yourself all day!). Good luck.