Hi, I’m Adam and am one of the owners of Access Techniques. I also wrote the IRATA training scheme and am currently chair of the IRATA training committee which also gives me a seat on the IRATA exec.
The role of Level 3 is team leader on site. They should be responsible for implementing the method statement (and rescue plan, if required) and identifying additional site hazards that might require changes to them. While the average Level 3 has not been trained to write risk assessments or method statements, some of the more experienced ones may be able to help you. IRATA are currently trialling a safety supervisor course but it is only to formalise the above as the current training is mostly practical.
Doing it in house also means managing your own equipment which requires additional time and expertise particularly with chemicals involved.
Are you using a contractor currently? Do your staff have particular skills that a contractor wouldn’t? I would suggest looking at that as a first option - I can recommend via pm - even if the plan is to use some of your own level ones and transition to doing it all in house eventually.