I think you should go for award tickets for all 3. J there and Y back would be 240K unless the return trip is before May 15, in which case you'd save 30K miles. You can't book premium economy with miles so best to decide between J and Y. I am a complete novice on upgrading with miles so I'll leave that to others.

Amex Platinum Int'l Business CO requires refundable J ticket so I would guess it's cost prohibitive.

Your options for US-Europe are AA, IB, AB, and BA (which you will avoid due to high fuel surcharges). Unfortunately only BA flies to LUX, so you'd have to so something like MSP-ORD-MAD-LHR-LUX where you are flying BA just for the last leg or two. Alternatively you could fly to FRA, DUS, or BRU and train to LUX. Then you could have a simpler itinerary like MSP-ORD-DUS. The NUE leg is a little easier as AB should be able to connect to NUE more easily. Basically I would rely heavily on AB since you are flying to Germany and surrounding. If IB has availability though, it might be worth taking it though it would nearly assuredly add a stop. Good news is AA allows routing and date changes for free, so take what you can get when you can as long as it's minimally acceptable and look for improvement. I recently flew CLT-LHR direct, but I booked 7 months in advance on IB CLT-MIA-MAD-LHR, then switched to CLT-FRA-LHR about a month out then got the direct about 3 weeks out.

IB availability won't show on aa.com. I'm sure KVS gets it but I've never used it. Or you can use qantas.com or Iberia.com to see it.