I kind of feel like this is one of those "Photography is easy, you just buy a camera, some lenses and photoshop and BAM! You're a photographer." I have a lot of those cameras that those people bought. I relieved them of the equipment when they realized that it's not that easy at a MUCH discounted price.

Thank you, very much!
It's not easy nor is it as cheap as purchasing a good camera and lenses. Most people look at the cost of a custom photographer and think "they're rolling in the dough, that's ridiculous." We're not rolling in the dough. We're struggling most of us.
First there is education. You don't want to go back to school and that's fine. You don't have to. You do have to get an education somehow, somewhere. Where and how is totally up to you. There WILL be time invested and probably a good amount of it. There are webinars, seminars, web classes, classroom classes, mentorships, books galore... It doesn't matter, but you have to get the education in photography. Exposure triangle is easy enough to figure out, but mastering it and then mastering the use of light and then controlling light and then using strobes and modifiers and the list is almost endless.
After or during the education in photography you will also need an education in: Accounting (probably 95% of professional photographers are either freelance or self employed); copyright law (it's incredibly complicated and in your country you don't own your copyright if you are contracted by a client to take photograph); contract law (EVERYTHING must be in a contract-it's complicated); marketing (you don't work for a company that pays you a salary, you have to sell yourself); web design (those pesky websites are complicated as hell!); general business education (you're in business for yourself now!); IT and computer management (let me say that word again... COMPLICATED... back ups and secure storage and Raids and computer specs and calibration and IPS, TN...); and the list goes on and on and on. You can absolutely do it any way you want to. I will suggest that the photography education and the business education be the best you can possibly get. A poor business sense will destroy a phenomenal photographer and a mediocre photographer can succeed wildly with good business practices and good marketing.
Back to the it's not cheap part of that statement up there... You're saying BUT! A D700 isn't cheap. Nope, it's not a D3100 at $450, but it's only a drop in the bucket to what you will be needing. Make that 2 D700's-your whole business is 100% dependent upon your camera equipment. If you happen to break one or one malfunctions during a crucial shoot? What do you do? Sorry, joe client, but you'll have to wait 2 weeks while I get the camera repaired. And so will every other client that you have booked. And the bills still have to be paid while that camera is down. You can't go back and recapture time. That money for that two weeks is GONE. Yes, you can shoot that client later, but then you are pushing back OTHER clients... You lost the time and money for that two weeks. For me? That would be more than that second D700 would have cost.
After about a month of shooting with that D700 you will quickly realize that you need some light. A speedlight $500 more. Studio strobes $1000. On location/battery setup for those strobes? could be another $500 to $1000.
We haven't mentioned lenses: The two minimum would be the 70-200 f/2.8 VR at $2500 and the 24-70 f/2.8 at about $1500. Now those may not be your style and you may well choose a lineup of primes which will run you less than half of each of those lenses, but you'll need several of them so you are back to the same amount of $. And then there is the backup lens for your most important ones. Same as with the camera... if you're without you are screwed. AND the back up for the speedlight.
Let's now touch on the expenses of business-licensing, insurance, contract review by an attorney, accountant, software for tracking your business, marketing, utilities, rent/mortgage, vehicle expenses, memberships, websites, internet access, proofing... The list is extensive. My studio is in my home and my expenses run me about $1000 per WEEK. I average about $1800 per week take in to only get about $600 to $700 in the end. I don't have ANYTHING elaborate and I don't have the best of anything.
I mentioned education-no matter how you get your education it is going to cost you money. You may be able to do it very cheaply, but it will cost and cheap is relative... It's not $100 no matter how you slice it.
Here's a good couple of links on the cost of custom photography:
How to Price Photography - Timothy Faust Photography
Why are Professional Photographers so expensive?
I am not saying this to discourage you. You can absolutely become a professional photographer. Just do it with reality in your head.