PRP,
Congrats & Thanks for sharing your final configuration.
Your thread and a few others really helped me makes decisions for our order.
Let us know when you get it and how it works our for you.
Based on your workflow description I think (and hope) you'll be very happy with the i5.
I also think you'd be fine with 24GB by adding 16 to what's already in there.
If you decide you want more later, price will inevitably drop.
(paid $115 last year for 16GB kit that's now often $79)
As far as memory goes, I'd advise lots of grains of salt if you try to take in that RAM thread.
My advice after lots of reading: Save grief and just order memory that matches the spec Apple provides.
I'm ordering ram for 4 iMacs from Amazon: Crucial CT2KIT102464BF186D
Right now it's $88 per 16GB. (It's same sped, speed, and class as stock)
In my experience with many dozens of Macs, memory upgrades can be inconsistent.
I've had an MBP balk at RAM that was faster than factory spec,
while an _identical_ MBP ordered/received at the same time took same dimm gladly and still runs grrreat.
Best of Luck