This is pretty much exactly what I am looking to do in the next few months. My clientele has grown and is continuing to grow and I have extra space to run a second treatment room.
My advice, is to wait for the right person to come along... Despite moving to a bigger suite, I was prepared to stay solo until I found the right person, since the wrong person can ruin your business. I happened to interview the right person the day after I moved in here, but I was prepared to go another year if that's what it took.
Just 10 weeks after she started doing electrolysis for me, most of her (part time) availability is already full, but she's about to make the leap over to full time and we're expanding to offer full salon services too, since she's already a licensed cosmetologist and we have plenty of (particularly trans) clients that would appreciate those services, plus she'll be bringing a lot of her existing hair clients with her. I may look to expand again later this year in preparation for next spring's electrolysis rush and/or more hair styling clients.