I started (aged 15) by being a 'gopher' for a portrait photographer back in 1961, it was a lot easier then as not many people had decent gear and film was 'alchemy' to most. My grandfather was a photographer so I knew how to take good images.
I was forced into starting up on my own when the photographer I was working for had a heart attack just a few years later, It was lucky for me as He gave me His business in the centre of Sheffield here in the UK. But most of all He gave me his contacts. Photography is more about who you know and not necessarily what you know, unfortunately.
Using these contacts I got into Corporate photography which is what I did for nearly 50 years, till I too had a heart attack and retired.
Corporate photography is where the big money is, the work is well paid and keeps coming, you are fulfilling one contract after another and it's varied which was brought home to me one week when I was taking shots of rivets in my studio for a trade catalogue on the Monday, on the Tuesday and Wednesday I was photographing models in Paris for Coty, and on the Thursday down a coal mine in Wakefield for the then National Coal Board.
I'm sure you realise that this part of the business is solely dependant on your reputation and the quality of your images, I spent almost as much time getting the rivet shots right as I did on the shots of the models.
I have a studio, mainly for product shots, but I have had to take portrait work from time to time, I always charged for a 'package' of 3 to 5 images. I always supplied prints and would never supply the original files.
The Corporate photography was different I supplied the files with 'any use' contracts, but always kept the copyright, which is a pretty standard way to do business. The prices varied depending on the use of the images. The Coty images were used all over the world and were printed many times, my price reflected this (5 digits), the rivets shots were much cheaper of course! LOL.
More photography businesses fail due to bad business practises than bad photography. The photography is the easy part. You'll spend far more time keeping the Tax Man, Accountant and the Bank Manager happy than you will taking images.
The important things are
Cost out your expenses, you have to know exactly how much it's costing you to get to a shoot and price accordingly, at least double your expenses, leave nothing out, not just fuel, insurance and road tax, but servicing your vehicle, MOT (UK), depreciation on your gear and vehicles etc. etc.. It's always costs you more than you think it does.
Get a good Bank Manager and Accountant, they can save you money. There will be times when you need £1000 quickly that you pay back the next day, always look to see that you do, then similar funds will be available at any time which is really useful, the Bank is backing you, it takes time to build this relationship, not all Banks are good at it. Your Accountant can save His fee (and more) in Tax if He does His job properly.
See this answer I gave this morning on web space.
You won't make much, if anything, from direct sales of your images over the Web. Pin money at best. Don't spend a lot on it for that reason, it's more useful in getting your name out there advertising your products.
A lot of seasoned Pro's make as much money from running Photography courses as they do from their core business. With the explosion of good quality digital cameras around there are a lot of people that soon realise that owning a decent camera doesn't guarantee good images, that's where you come in. Turning a modern disadvantage into cash. People will pay £80 to £100 for a days specialist course, lunch extra. I limit numbers to around 12 people as that gives them a good deal of one on one and I have run a Portrait course in my studio many times, a good way to get extra funding as you need it. Returning customers make up a good proportion of my clients so I must be doing something right. I pay for the model usually around £150.
A variation on this is to use local attractions such as steam train locations etc. and run courses in association with them. They are usually staffed by volunteers and welcome the extra funding.
This is a market that is expanding.