I spent 5 years running my own business and fell flat on my face. I worked harder than ever before and never had any money. I ran up $30,000 debt. I spent the next 5 years working for someone else and paying it off.
What killed me was....
No help. I did get friends sometimes when available and a couple of temps from an agency. Mostly I was alone, working both ends and the middle. I wore myself out. I was 51 when I started, well past my physical prime.
Disorganization. I didn't have a good work truck most of the time and had a hard time keeping material organized. I'd run out of simple stuff and have to keep running out for stuff I should have had on hand. I also didn't stay on top of my job accounting and lost track of profit and losses.
Underfunded. I could only pay for general liability insurance and a ghost policy for workers comp. Most commercial customers won't deal with you with a ghost policy. My few small commercial customers didn't think to ask for proof of insurance. You really need standard coverage, which is very high.
Delays on quotes. I was usually good at getting quotes back quickly but I missed the boat more than I should have. I would get home and crash soon as I sat down. Then I would get busy next day and let too much time go by getting the quote out. Best to do a quote on the spot if you can, next day if not. FORCE yourself to do this. Also, my last year, I was totally worn out and forgetting to keep up my planner. I missed a few appointments and lost chances at several jobs.
The economy. I started in 2008 when things were getting tight and they got worse from there. I priced work cheaper than my previous 2 bosses and still couldn't get but 3 or 4 jobs out of 10.
Not having a website. For a while, I could not afford it at all. Then I found a provider who could sell me a simple site for $300 something. I paid for it and then couldn't figure out setting it up. It was a do it yourself thing. I tried to get my older daughter to help do it but it was a bad time in her life and it didn't happen. If you start up, do get a website. People used to consider you legit if you were in the yellow pages. Now they consider you real if you are on the web.
I was pretty good at not taking on bigger jobs than I could do. I was not afraid to refer out projects too large or too complex.
Is it possible/practical for you to start off doing side work? That is a good way to hone your business skills while still having a paycheck. Take jobs your boss isn't interested in. Learn to track your expenses per job and see if you can make a go of it. Also, see how many of the boss's jobs you can do without having to call for advice/direction. If you can do most jobs on your own and learn quickly the ones he has to help with, you can probably manage your own shop. If you can do the planning and accounting too, you will be OK.
The little bit of payroll I had, I did through a payroll service. I knew I would lose track of tax withholding and get in major trouble with the IRS, so I had them do it. One of the few really smart things I did.
I hope it works out for you.