Nicely written! I can tell you've put a lot of time and thought into this. I'll critique, but know that it comes with respect for the hard work and thought you've put into it. Here are some problems I see in the argument:
1. It's possible to talk and reason about a concept without having a precise, rigorous definition of the concept. — icosahedron
There is something implicit you are leaving out. "...if the goal is to ultimately discover what that rigorous definition of the concept ultimately is."
We start with the ephemeral and try to make it clear. That's the point of good philosophy. If we keep terms general and wishy washy based on a person's personal opinion, we're talking about loose subjectivity. At that point, we just stop wasting everyone's time and say, "Believe what you want to believe". But that's not rigorous thought or rationality. That's just giving up.
2. It's meaningful to talk about free will. — icosahedron
What is "meaningful"? You gave examples of what some people conclude free will is, but why is it "meaningful"?
People understand what is meant by free will, which is why they are able to have meaningful discussions about it. — icosahedron
Here is seems you are equating "meaningful" with "People understand what it means". If people understand what it means, then why is there a discussion and debate? The problem is many people do not understand what it means. Free will is an often addressed question on these boards. I would clarify what "meaningful" means in this instance.
In grade school you have probably reasoned about numbers like 1,2,3, and how they interact. Did the teacher provide you with a definition of these numbers? No. You intuitively understood what they meant from examples. — icosahedron
This is an example of a mistake you repeatedly do in your proposal. You are assuming people act, think, or have experiences in a particular way. Don't ever do this in a proposal. People don't think, act, or experience things the same way.
When I learned to count, my mother taught me using each finger to represent the number. There is nothing intuitive in matching the number "3" with the concept of three. Without being taught to think about the number 3, a person may very well just have though, "a bunch", and never conceived of math. I used to teach math for five years. If math concepts were intuitive, I wouldn't have needed a job. =)
If some fact or statement is immediately perceived to be true then it's reasonable to believe the statement unless you have a valid reason to doubt your perception. — icosahedron
Sure, no problem here. The problem comes into play when you think on it a bit longer, and start to get valid doubts on your perception. Free will for example. Many people think they know what free will is, then have an idea that puts doubt into their minds. If free will was still perceived to be true upon further reflection, then very few would question it. The fact that you had to write a paper showing why free will is intuitive and true, is evidence that it is not so cut and dry.
In this argument we have already achieved something that I've never seena anyone else arguing for free will achieve before, at least not explicitly. We have completely turned the tables of the argument. We made it so that the burden of proof is on the objector of free will to give a valid reason to doubt my perception of free will. — icosahedron
The argument has been made before, but it is a good strategy. =) I don't think you need all of the leadup for this though. You can simply state, "Look, free will as I perceive it works well for me. Give me a valid reason to doubt my perception of free will in a way that also works well for me." Start from there.
5. There is no rational reason to prefer determinism over indeterminism. — icosahedron
Then you do not understand what rational means. Rationality is using stable concepts to concretely understand the world with as little indeterminism as possible. Its the use of deduction, while minimizing induction.
Quantum mechanics does NOT show that the universe is indeterministic, but it does destroy all hope to prove determinism through laws of physics. — icosahedron
I think you're misunderstanding quantum physics. The only reason we are able to use it is because we have found deterministic limitations within the indistinct. We have deterministic conclusions that we cannot measure a quantum states and velocity at the same time. This allows us to accurately and reliably predict how things work. This is why we have cell phones that work consistently.
Unless you are a scientist, don't use quantum mechanics in your philosophy examples. Its to easy for non-scientists to attribute mystical qualities to it, when that's not the case.
6. Answer to the objection "But determinism does not give you free will. It only gives you randomness, and free will cannot arise from randomness, nothing about randomness is free, it's just random." — icosahedron
I don't have this objection, so am skipping it.
7. Answering the Sam Harris objection about predicting our choices before we become aware of them. — icosahedron
A good answer. I agree this objection falls flat.
Feel free to counter or point out where I've misunderstood your points!