Just a short note on book publication.
It can take a very long time to get an "unsolicited" manuscript to an editor to have it read. My co-author and I didn't have an agent, but we did have a connection who got our manuscript to Dell Publications.
The manuscript was read twice by the editor and once by his assistant. The editor got it and the assistant didn't (she didn't understand the point of the story at all). It was returned to us for editing and changes, but what was wanted was never made clear. We did some work and sent it back to the Editor, but it sat for a long time and we eventually requested to have it sent back.
That was almost 25 years ago. We still have the manuscript but have never done more about publishing it. I believe that the editor we dealt with is no longer with Dell, so if we had the stamina we could begin again, but neither of us does. In fact, I haven't even seen or spoken to my co-author for over 15 years, I don't know where she is.
This past year, I decided to hire a lawyer who deals in intellectual property so that I could do some work on the manuscript and not have all of my effort benefit my co-author who, it would seem, doesn't care anymore. I am sure, though, that she would care if any money was made from the manuscript whether she worked on it or not. So far, I haven't gone any further with the project.
If a publishing house likes your manuscript and decides to publish it, they will pay YOU. But you may need "the usual folks" to proof read and fact check (if it is non fiction) and it is probably a good thing to have an agent who will take a percentage of the profits for payment for the services that an agent provides.
It would be great not to have to pay an agent, but "unsolicited" manuscripts sit in large bins in the offices of editors all over the world and if yours is in that bunch, it may never get read at all. Fiction is probably the hardest to get published but I have a non fiction manuscript (in addition to the historical fiction that Dell saw) that I have never submitted, so I truly can't say.