I think it will depend on your customers whether they choose to go with you or a cheaper tech & the difference in your work. Some people will always go for the cheapest option but many will shop around for the best, you need to figure out how choosy your clients are.
If there is a significant difference in ability then you will get your regulars sticking with you practically whatever you charge. However, if the other tech is pretty much at the same level as you then most people will not pay more for the same result.
It's a bit of a tricky situation as you obviously don't want someone who is bad as it will put customers off but if you want to have different levels then the other tech won't be up to your standards. It's a good idea in a large salon with lots of techs but if there's only 2 of you & both are qualified, it could be difficult to organise. I would make sure you think of the long-term options before you take on another tech. I doubt another tech would be happy sticking at a lower level forever. How do you decide when they qualify to raise their prices? Are you basing levels on training or experience? What happens when the other tech does extra training or gains more experience?
If you have too much work to carry on by yourself, perhaps you could bring in somebody part-time to see how it goes?
HTHs
Regarding the question about trainees, I would say that they definitely need insurance if they are carrying out any form of treatment.