I started in business in 1993 with a manual total station, so I hired couple of part-time assistants and trained them to run the gun so I could attend to the tasks at the prism pole. By 2001 I was down to one guy. He didn't really have an interest in making surveying a career -- he had a degree in wildlife biology and really wanted to work for Fish & Game, though that never happened -- but he was smart and reliable, so I could put him behind the instrument and get a lot of work done.
In 2001 I bought a new Ashtech ProMark2 system (L1-only). It was great for getting on the grid and setting control on large jobs, but it didn't otherwise change the way I operated.
In 2002 I bought a used Ashtech Z-12 so I could reap the benefit of dual-frequency GPS. Again, it was great for large-scale control (and doubled as a space heater!), but my workflow remained pretty much was the same.
Over the next couple of years I added some Trimble 4000SSi units so I could do height modernization projects. Those jobs were interesting and paid well. I used project owner (public agency) staff as observers, so I didn't need to hire more employees.
In 2009 I bought a used Geodimeter 640S Pro robot to dip my toe into one-man crew country. It worked, but was pretty cumbersome to set up and run, so I only used in on a handful of small jobs. But it made me realized that a solo operation was a realistic possibility.
In 2011 I bought a used Leica TCRA1102plus (got a great deal from a former employer), and started doing some larger jobs with it. It was a bit clunky to set up, but was very accurate. By this time my assistant, who had been with me since 1997, was gaining more expertise and responsibility at his other part-time job, so scheduling him for field work became more challenging. The Leica allowed me to work when he wasn't available.
In 2014 I added a Triumph-LS / Triumph-2 system to get a taste of what RTK had to offer. I introduced it gradually to my workflows, but it made some jobs possible that I couldn't efficiently do before.
In 2015 the Leica began to have occasional glitches, so I bought a new GeoMax Zoom 80. By this time I was doing most jobs solo, working my part-time guy only occasionally. I still relied (and still do rely) on the robot for urban boundary and topo work, but I do use RTK for site control a fair amount.
By 2016 I was fully solo, and haven't had any employees since. I hung onto my Workers Comp coverage for a couple of years just in case, but eventually dropped it.
My point in all of this is: if you're able to work without employees, do it. Life is much simpler that way. Not everyone is cut out for solo work, and not all job types allow it (jobsite safety can be a problem), but it sure is nice to have the flexibility of working when you want to, and not having payroll to worry about.
With regard to part-time versus full-time, I can't offer much insight. I never had a full-timer, and wouldn't have wanted the responsibility. My goal was always to be a surveyor, not a manager, so I deliberately stayed small. But after a couple of slow years at the beginning, I've always made a comfortable living, and though I'm well past "normal" retirement age now, I still enjoy doing what I do, so I continue to do it.
Good luck, whatever you decide!