Richy
I worked in the Taxi and Courier trade for years, all the drivers are self employed.
In the taxi trade the driver provides his own vechicle, but some taxi companies do rent these out as well, the taxi driver pays a weekly radio rent and he is put on the rank and allocated jobs on a rank system, all the takings belong to him.
The courier driver also provides his own vechicle but is either paid a milege or commision of the job.
Both of these only work for one company and the taxman accepts that they are truly self employed.
You might want to look at this method.
The other way forward is look at your strengths and weaknesses, you seem to be good at getting work, but fail at the admistration and window cleaning side.
Why not get in a general manager who runs the admin and cleaning side of the business, while you consentrate on what you are good at which is getting the work in.
You will still need to sit down with the general manager to know what is happening in your business, but leave the running to him.