Ok, I'll try to keep this short and fairly simple.

Try to estimate in todays dollars how much you need to live on. That's easy to do as you can figure up how much you lived on in 2003.

However, in 15 years you will have a different situation. Your kids will be older and you will be in a different house.

Anyways, once you know how much you need in a year, you need to save approximately 25 times that amount.

Let's say you need $50,000 to live the kind of life you want to live. That means you need to save up $1,250,000. Using a safe withdrawal rate of 4%, that means you can safely withdraw $50K a year without fear of running out of money.

Ok, I am keeping that simple as there are more variables, but that will get you started.

You mentioned starting a business. Is this the kind of business that will keep going after you are FIRE'd or is it one you can sell or is it one that you will stop when FIRE'd? Ah, I just read it again and you would like to run this business when you are FIRE'd.

Do you have any pensions or any other guaranteed income?

Let's say you only have the money you save up to retire on. Let's assume you need $50K a year. Let's then assume you want to save up 1.25 million.

How do you currently invest or how do you want to invest?

I would recomment investing in the stock market and possibly in real estate.

Stocks can be simple to invest with because without knowing much at all about investing you can easily open up an account with Vanguard and then put your money into the account to buy and index fund.

You can buy real estate via a REIT or you could buy rental property.

You can also buy individual stocks if you think you can do better than an index fund will do.

Ok, let's say you have a successful business that brings in 20K a year. That means that you only need to provide for 30K from your pot. That means that 30K times 25 equals $750,000 that you will need to save up.

If your business brings in 35K a year, then you only need to provide for 15K. That means you will need to save up $375,000.

I hope my post is helpful a little bit to you. If any of this at all is confusing, just ask questions and myself or someone else will explain.

Oh, I'm assuming you know a little about investing and compound interest. If not, just ask away.