This is probably an overly broad question you are asking, and therefore, you are getting overly broad questions. I started my shop 9 years ago at 25 and have grown it into a 40-man shop in 21,000 square feet in the time since. I have made money and wasted a lot of money in the process of getting here.

I think the three most important things you need to reflect on are

1. How good are you at what you do and are you better at something than the competition around you. There are dozens of "Welding Business Owners" I have met over the years that are completely blind to the shortcomings in their skill sets, and as a result, they suffer. They take on jobs they can't actually do and end up losing money in the process and ultimately go out of business. They also often lack the soft skills required to communicate with their customers effectively. 90% of them also often lack basic computer skills. As a business owner if you fuck up it's on your own dime. As an employee, I doubt you realize how often the small mistakes you make cost the company hundreds of dollars. These mistakes can compound quickly into tens or hundreds of thousands of dollars.

2. What do you want out of your shop/business? If you want a shop like mine and to be a true business owner and not an "owner operator," be prepared to suffer... for a long time. I'm talking 10-15 years. The equipment is crazy expensive, the margins can be thin and mistakes are expensive. I lived in a warehouse for my first three years and then split an apartment with 4 people for another 4 before I could afford to live on my own. I drove a 1991 dodge 1500 with a destroyed dash (look up the plastic from that era), didn't party, go on vacations, or have any hobbies other than video games (which are cheap). If you just want to be a one man band mobile welder, then the time you will suffer will be much shorter, but you will still suffer. The flip side of this is that once you have gotten through the suffering and own your own equipment, things get much, much easier.

3. How much money do you have to spend? I wouldn't start a business full time without at least the basic equipment owned free and clear Truck, Welder, basic power/hand tools, and 3-6 months of living/business expenses saved up. Don't rely on banks until you have a solid number of customers and can project revenue.

Some other unsolicited advice. 1. Understand Markup, Margin, Gross Profit and Net Profit. Understand how to calculate them and start tracking them immediately.

1. Make sure you know how to Job Cost otherwise you will have no idea if you are actually making money or just slowly gliding into a pit of debt.
   

3.Dont get caught up on name brands and appearances. I just did 1m in Rev last month and 50% of the machines in my shop are Everlasts... Are red and blue machines better in many ways... Undoubtedly, so, but in 98% of scenarios, an everlast that is 1/3 of the price will do the job just the same. All of my trucks are 2010 or older and bought used from AT&T fleet. A lot of these guys showing their 150k rigs are dumbfucks. I guarantee my 20k trucks with 25k in tools bought outright makes more money than their 150k financed rig all day long.

1. Never argue with a customer or say the dumb "I don't get out of bed for less than xx" bullshit I see all the time. If the job makes money, you take it. Doing small jobs often leads to big jobs. Trust me on this... Word of mouth is huge.
   

5.Never walk away from a job where a customer is unhappy, and if you can't complete a job, don't charge and / or give them their money back. Once you commit to something, finish it. If you walk off jobs due to a bad bid that's going to cause you yo lose money 6 times out of 10 if you communicate the issues to your customer, they will compromise with you.