The roller I’m looking at has a port for tuning water height, and also has emergency drains if it fails. If it were to fail in that way, it would just translate to the filter roller effectively turning into a second spillover chamber. Don’t think that’s too big a deal considering it’s still in the sump.2 - You need a way for water to bypass your filter roller for WHEN it fails and becomes clogged.
As for the rest of your points, yes, I’m planning to run a proper complete sump, despite my diagrams not showing the skimmer fuge and return chambers. And so the skimmer water height will remain stable as well. And I’ll have my ATO sensor in the return pump as per usual so that should be a non issue with evaporation as well.