Q3a. How can a wrong understanding of determinism and predestination keep us from the kind of gutsy prayer that Moses prayed?
If we think that everything is predetermined then there is no need to pray. We simply need to keep waking up every morning and life will play out like it is supposed to.
Q3b. What do you call a belief that our prayers make no difference to God's response?
Lack of faith. We are told repeatedly to pray and that if we believe it will happen, then it will happen
p/s I don't know if this will help anyone else come to grips with pre-determinism, fore-knowledge and free will, but the closest thing I can think of (in human terms) is chess. If a master chess-player can foresee his opponents available moves and his own available moves up to 3 or 4 or more steps ahead, I'm sure our omnipotent and omniscient God can foresee all the available moves of all mankind through until the end of time. There is one big plan for overcoming evil and redeeming mankind, just as a chess player has one big goal towards victory over his opponent. There are laws of the universe (science if you will) that governs all living and non-living things, as there are rules to the moves chess pieces can make. Sure the moves we humans can make are infinite (to our human minds), but to God, infinite possibilities are nothing. So we are free to move, to sin, to obey, to live, to love and most importantly to pray and ask for intersession, as we see fit, but in His infinite understanding, God can still make his plan work around all the infinite choices that all human kind makes.