You seem like you are nearly there on sorting out a self emloyed position where you are, with only 2 minor issues that I can see.
The first I can see is only working for one person - Possible solution: you say you have a Wopa crush and foot trimming tools, many farmers now outsource routine foot trimming, make sure you are NACFT qualified and foot trim a couple of smaller local herds, you may only spend 4-6 days a year doing this, leaving plenty of time for the herd managing job, but gets you round the technicalities of employment.
The other is the pay issue - May be a bit more tricky, you need to ensure that you are paid based on doing a job, rather than an hourly rate to avoid having to be employed, but to ensure you are getting a fair deal it needs to reflect the amount of work required. I myself would favour a payment of £x per cow, per year / day, + a simple bonus scheme to reward effort and achievement based on the goals of the farm. e.g a payment of £x per extra litre produced from forage, a payment of £x per extra cow in calf over the previous system.
What I meant earlier about stability was meant to be more subtle than moving employers regularly and a hugely fluctuating income, more, things like a problem causing you to be late finishing in the evening because you have to finish a job, rather than going home at a set time, whether the job is done or not.
I hope I may have been of some help to you.