On the business side:
1, most states you can start a business for small money, $50 or less. Start out as a 'sole proprietor' which means you will use your social security number. The IRS will track it this way, any accountant can sort it out in 30 seconds or less. Down the road you will want to spend a few hundred dollars and incorporate. This is primarily for liability reasons.
Say you repair something and it goes wrong. If they take you to court, they are litigating the corporation, not you. Protects you and your family.
2, very much related to this, get a minimum or better liability plan. This protects you in case you get hurt on the job and can't work at all. Also, if you get sued it kicks in and protects you. What I am describing are actually two different types of policies. The first one is Workers Comp, and in some circumstances is required at all times. It get's expensive. If you have an office job, they measure very little risk of you getting hurt. You work on engines and could possible ruin a finger, a bigger risk.
The second is a basical business liability. Chances are it will be pretty inexpensive. My wife used to clean businesses where should could break things or use a cleaner that ruined a floor. Her liability insurance would ran a few hundred dollars every 6-months. Some states may require a bond or allow for either. Go with insurance, not the bond. Bonding becomes a bigger liability and is used for bigger companies with large asset pools.
Get these two small steps taken care of, maybe $100 the first month then off you go. There are some great ideas on here but small business is America. Over 80% of Americans work for small business. Best of luck on this!!

Boo