I started flying LAX <--> ORD a lot, and can usually find flights on Dreamliners (or other planes with lie-flat seats in first class) that work. A decent percentage of the time, I'm able to upgrade for ~$300 which is usually worth it for me. This price seems to fluctuate wildly though - $600, then $400 an hour later, $900 the next day, etc. - it does seem to be roughly related to the price to buy the first class seat outright though. I'm wondering a few things:

1. I'm sure this is not close to being completely reliable, but does the upgrade price have anything to do with what I paid for my economy ticket? Or just the current difference between the economy and first class fares?
2. If I pay for economy plus, does this affect the price to upgrade to first class? Some of these planes have the "premium plus" seats, which I can upgrade to for $100 - never sat in one so I'm considering that. Would that be refunded if I later upgrade to first class (or would I get a lower price to upgrade to first)? I don't want to pay $100 for E+ and then another $300 for first if I could have just paid $300 to upgrade from economy to first.
3. Tangentially related - I know I get PQP for the first class upgrade price (or any preferred seating charge). I'm considering buying one of the "bundles" to upgrade to economy plus because it's a decent amount cheaper than just buying the economy ticket and paying for economy plus. Will I get PQP for that bundle upcharge as well? I figured I would, but then I realized that some bundles include things like lounge access and wifi, which I assume don't earn PQP. Are they smart enough to somehow prorate the bundle charge and only give me PQP for some percentage of it in those cases?

Thanks.