Hi, I have been self employed for the last 6 years doing more or less exactly what you plan. I'll make no bones about it, its a hard game on your own with only one machine to run. The worst part is trying to build a buffer of cash to smooth out the cash flow.
I think the basic things are:- 1 Get organised, know where everything is and that its usable. 2 Buy the best machine you can - old kit is cheap for a good reason. 3 Things start to make sense when you have 2 machines. And finally do your best not to rely on only 1 or 2 customers.
Diversify as best you can.
A personal bug bear of mine is that everybody wants there stuff for nothing and they don't know or care about the investments you have to make in engineering. The odd £70k for a medium size VMC, all the tooling that goes with it not to mention software. Consumables like cutters and drills etc. It really does add up.
I hope I haven't pissed on your chips too much. After all said and done I can't see myself with a "proper job" ever again. Good luck and don't let the buggers grind you down.