need an upgrade strategy for an AirFrance/Flying Blue award rez that includes a DL longhaul segment

I have found an AF/Flying Blue award that combines an AirFrance flight within Europe and a Delta longhaul back to the US. It's 55k Flying Blue miles for the economy ticket and nothing is current available in business. The same ticket is unsurprisingly available on DL right now for 375k SkyMiles (no thanks - would be 150k on Flying blue).

My plan is to snag the economy seat now and look to upgrade. I'm wondering if anyone knows:

• • Can I anticipate an at-check in option on Delta (or even better - now in the Delta seat selection!) for the Delta longhaul flight to upgrade and any estimates or previous DPs on what that might cost for a CDG-MSP leg?
• • Is there any way to Waistlist my existing Flying Blue award for business space, should it open up to avoid having to keep checking or signing up for Expert Flyer?
• • On that note, is there a predictable schedule when Delta releases premium award seats to partner bookings if available? (2w out? 1w out?) or is random?

I'm schedule constrained so it's this flight combo or no-go so the upgrade or suck-it-up in econ are my current two options. Would love any insights on upgrading or rebooking before this flight appx 6 weeks from now. 🙂