I'm concerned about being able to communicate my vision as a writer/director to potential producers and investors. Should I really spell it out in the script and include camera directions, notes for actors and crew, and other specific details, or should I let the writing speak for itself? It seems like screenplay rules say that you shouldn't include direction, but I'm not sure if I'm including enough information in my screenplay.

Or put more simply: How much direction is too much direction in my first script?

I think you're getting a little ahead of yourself.

Finding a producer and making a film is very hard even if you have some level of professional experience. The question you should be asking is this: How do I write a great story that a producer (and cinematographer, actors, etc) wants to help me make? How do I write a story that people want to give me money to make?

That's where your original question is misguided. Every day great scripts break one or two "rules." Your job as a writer (and director) is to tell the best story. Communicating your vision coherently is exactly what a writer does, and it's one of the reasons it's so hard to do well. But including a ton of camera directions or other unnecessary details will distract from that. I'll explain more in a minute. But first, a side note.

Producers aren't going to tell you to change a shot or a line of dialogue. They may give you notes and advice, especially if they're experienced, but at the level you'll be making films for the next ten years (or more) when you're just starting out, even that basic level of involvement will probably be more limited.

Here's why you don't want to include unnecessary direction or make it read like an instruction manual:

First, it may distract from the reading experience. If you send the script to a rich dentist in hopes of getting financing, she doesn't care about a dolly shot this or move the camera on that. She wants to know if she likes the story and likes you. To some degree, the same goes for actors, set designers, costume designers, and everyone else.

Second, what makes the filmmaking process great is that you get an amazing group of people together to do things they're really good at and work as a team. You may be an incredible writer and director, but I doubt you're also a world class cinematographer or production designer. Predetermining too much stuff in your script (and being too stubborn to change it if someone else suggests otherwise) takes away the job these people are paid to do. If you need to include a shot direction to communicate something effectively, then do it. But don't use it as a crutch because you can't find interesting and diverse ways to state a line of action.

It's easy to fall in love with things in your script. It's even harder than you think to cut them when you don't have people telling you no. Go ahead and fall in love with that witty line of dialogue you wrote. But is it really worth it to fall in love with the idea that a shot is a medium shot instead of a wide shot?