Your business model is nearly what supported me for 40 years. BUT I am a "dungeon" or maybe more accurately a "junkyard" type. And "bring me only the part you need worked on, clean", may work for enough customers in your area, but would never work in my extremely rural, timber-and sawmill-and farming area. My customers will often break stuff taking it apart. They work in the woods or on the farm, and have no facilities to clean parts. And, if I am to repair a shaft, or a bore, I have to have in my hands the bore or shaft it fits with, because the mfr's specs if available no longer apply, and if I ask a customer to measure it, I get +- a quarter inch. Here I HAVE TO deal with the whole machine, if I am to make it work again.
Customers will show up at 6:00AM and 10:00PM, with hay in the field or a 'dozer in a swamp. Their emergency does not have to be yours, but neither does their good-will.
"Find the rich customers and charge the moon and stars" sounds good if (a) they exist and (b) if you love money more than helping folks
Yes, you need a big lathe. You need a rosebud torch. You need a set of vees you can clamp on a long I-beam for indicating as you straighten stuff. 50 ton press is a good start, but I have needed bigger.
If making a living and becoming a pillar of your community, the guy people depend and brag on defines success for you, you are assured of it. If 7-4 five days and a comfy suburban lifestyle is your goal, it will be harder