First I would talk to your local DNR and ask them the same. Then get a copy of the regs for your state. Some states all you need is to apply for a liscence, others you have to pay... others... whatever... but find that out... Decide if you can and want to do this.
ADC work is NOTHING like trapping fur IMHO. If you can get away with only working for farms and large property owners then good for you, but most of those folk are not going to pay you what you need to survive just to catch some groundhogs or coyotes... they will probably do it themselves or allow hunting on their land, or simply allow trapping on their land and not need to pay for it.
So you will be working in Suberbia. You will be working with people in front of people and in the public eye. You will be in attics and basements, chimneys and shower stalls (yes), and you will be on roof tops and in back yards where kids will be playing soccer and dogs and cats running around. Maybe office buildings... who knows... That is part of the job.. you never know what will happen. So if you are alright with that then great, Now you have to get the money to start up. That is all you, How much do you need? You have to advertize in some way, and you have to be insured. You have to have at least one truck / suv / van... You have to have multiple ladders, generally a lot of cage traps, catch pole (notice I did not say release pole ) And there is a lot more that will be area specific. You have to have business cards and contracts and ... bla bla bla.. lots of stuff you won't think you will want or need you will. But that will all come with time. If you want to do it and are willing to do whatever it takes, then go for it. Get startup money and get insured and licensed and start advertizing... That is the basics.