I charge approx. £22 per hour in North Wales
Rates seem ok for normal plumbing work, but as you said
Changed a cylinder, changed a pump, ,two electric showers, one power shower, bathroom in hotel,
All requiring electrical minor works certification.
Doubt if any of the above have a minor works certificate.
No wonder prices are dropping in our area.
You are not doing yourself or other installers any favour.
There are far to many basic level 2 candidates passing out of college, and undercutting to get work.
I did go sole trader straight away.
Where did you gain experience from, college
As for establishing a large business, look around you, most large and well established firms in the area are struggling.
Also check out how many outside firm are working on Anglesey.