Thank you for your questions, Andre.

"Sam can believe whatever he likes"

Can he? What if he likes the idea of free will but just doesn't believe it's true? Similar to how some people might like the idea of there being a God but not actually believe there is one.

"1) Do you define un-free will as determinism? (or that one thing causes another, and/or that we are not agents who can, at all, effect cause?)"

We are part of the chain of causal events. If I throw a rock, my action is the cause of the rock flying through the air. But what caused me to decide to throw the rock?

You can say that my decision to throw the rock is the cause of me throwing the rock. But what caused me to decide to throw the rock?

Without me, and my decision to throw the rock, the rock would not have been thrown. But I did not make that choice in a causal vacuum without any influences.

"2) Do you believe that you and I are absolutely distinct and different people, or contrarily, that we are the same person in a way and that the you/me/him/her/fish-in-the-sea distinction is a persistent and necessary illusion?"

we are different but connected. But the me of today is different from the me of tomorrow. You and I will make different choices, but I make different choices today than I did yesterday.

"3) do you believe that only the present exists?"

I don't know. Isn't a more important question: what does science tell us? After all, my belief doesn't make any difference to whether something is true.