There's a 100K Citi AA offer though it has a $450 annual fee (not waived) and $10K in 3 months spending requirement. Also comes with $200 statement credit so net $250 cost. You're right that AA doesn't partner with UR, but you can book one-ways with United and AA. So you can use AA miles to book 2 tix to Europe and United miles to book the return. However, you have a long list of destinations so it's important to mention that doing one-ways eliminates the free stopover that comes with United bookings.

If I were you, I would sign up for the 100K AA offer, book 2 biz class one-ways to Europe. Then use 60K United to book 2 economy one-ways back (biz would cost 55k each at best, 70k each on a partner which is more likely, and you don't need to sleep on the way back so economy isn't so bad). Then you can look to Avios to get you around in Europe when trains are too long/expensive. Make sure to open an Iberia and British airways account now. Once they are open for 3 months, BA Avios can be transferred to Iberia Avios. This makes the Iberia flights cheaper in terms of fees. UR can be transferred to BA Avios, and from there you can either book BA/IB flights or transfer to IB Avios to book of it's cheaper.

For hotels, consider Club Carlson (apply to this one next if you're going to do it at all and read the thread on it beforehand - US Bank hates inquiries), Hyatt (2 free nights at Park Hyatt Paris?), IHG (80K sign up offer), and the Citi card you're talking about if it's the 2 free nights one.