Realize it will probably take 6 months until u get anything useful which is an expensive period, how many patients they need minimum to cover their costs(salary,vaca, CME, insurance, etc, how much additional staff (nurses, auths, front desk etc) will be needed to bring them in.
I have 3 midlevels in private practice with the third still training. My main PA helps with basic injections saving time for me to do higher level spine stuff and news. Good PAs will increase your practice revenue by hundreds of thousands per year by 2 mechanisms -them generating revenue, but more so it frees you up to do higher level work to minimize wait times. I routinely do 30 procedures per day and oversee all of them at 2 sites.
Obviously if employed how much $/wRVU are u getting of them seeing patients with taking on all the risk u are from having them see patients on your behalf. Either this model or ensure your employer is paying you ~25-50k/year to oversee them.