I've been through it many times. By the time we get here everything is pretty much how I want it, I'm just checking that the cover worked as intended and the PDF prints everything correctly. Which it rarely doesn't once you get a handle on the expected input for your POD partner.

So, output print standard PDF (InDesign has a preset that works great), use the Lulu tool to get sizing info for the cover, re-jigger the cover and submit both it and the PDF. The software at Lulu validates it and makes it available to buy proofs. Buy and wait.

Then I redline the proof and decide, if there are any edits, how much I care. :D

DTRPG POD is similar but with more waiting.