Cool ideas, voted to help you decide. Regardless of which one wins in the poll, though. I think you should do what you want to do.
Though I would really like to see "Just Metal" come to fruition.
A halloween one should do good, though Prime may be a better choice. Bricklink is better for that Lego G1 haul, but I wish you'd get more CCBS and/or technic. Just Metal? Seems better a choice than the unnanounced project.