I started-failed, started-sold and currently run my own business. I have been running my current business for 14 years now.
I would assume you are young being in the military, under 30 perhaps. You have time. Take it slow, do not borrow a bunch of money from a bank or family/friends. Start part time from your home and let your business grow naturally.
You will learn quickly where your niche is and what products to sell. You may find that after starting, the money will be in vacuform accessories instead of kits, or custom one off parts or you may find 3d printing is the way to go. Just go slow, do not force it by buying a bunch of equipment on credit before you know if there is a demand.
No need to pay a lawyer or service at the start to create a legal entity, or pay for an expensive website or register as a business. When your part time endevours can match and more important exceed your full time income, not sales but actual income you can draw from the business after paying all monthly expenses, that is the time to decide to go all in and get a corporate entity etc.
I have seen too many startups spend a bunch of money on lawyers, developers, websites etc before making one penny of profit. Who cares if you are an s corp or c corp or LLC if you are not making a profit.
Also there is a difference between making money and making a profit. Amazon has been in business for over 20 years and is only now showing a profit. Moving billions of dollars around is not making a profit, its what you hold onto that is the difference.
Find your local Score chapter. Just do a seach for local Score chapter. These free groups are full of business owners who are willing to offer advice on starting a business.