Yah, iron heats up slower, but holds heat better, which lets me slow down my casting rhythm a bit, as opposed to aluminum. Despite being heavier, I find iron to be less fatiguing, therefor.
VPI paper will protect a mould for a while, but not forever. Last summer I opened up one that had not been used since about 2009, and there was a light frosting of rust. The inhibitor chemical had all evaporated away. Not fatal, a light lapping with 800 grit restored it, but I won't count on VPI again unless I also seal the mould airtight, as in a Ziploc bag or something.
BTW the glass jars the Smuckers Natural PB comes in are perfect. I store my Ed's Red in them, because even acetone can't get past that seal.