When I say gear, I don’t just mean the camera. To offer a professional service one needs a damned sight more than just a good camera. Tripods, lights, flashes, filters, reflectors, umbrellas, a second camera body. To paraphrase Matrix: We need lenses, lots of lenses. I agree that an 85 or 135 is a good early buy, preferably with a wide fastest aperture – the 85 f1.8 would be cool, especially as the 85 f1.4 is twice or thrice the price. A 50mm f1.8 would be useful too, as some shooting sessions might be in more enclosed spaces that wouldn’t suit the 85. The 135 is also very expensive, and to begin this career path it would be adequate to crop the 85 to get similar results.
As for Pentax being at least two steps downgrading, I’m not too sure about that, even though I agree that the D800E is a super camera. much much more than adequate for the purpose. Tis a pity the appropriate and necessary lenses to match that camera will be so very expensive.
To the OP, this is a major step, and needs a lot of prior investment of time spent in both research and building your portfolio. But decades ago I would have been happy to begin my portfolio with shots as good technically as many of yours are. Good luck, and if you get rich you owe us 10% ok?