I’m looking to fly EWR-LAX in June in ideally Premium Plus for 2 people. Neither of has any status with United. I also have about $250 in Travel Credit that I’d like to use as well as many Chase UR points. Two questions:

1. If I purchase a “Mileage Plus Upgrade Award” for $402 + 8k miles and be added to the “upgrade waitlist” what are the chances if any that I would actually be upgraded? Right now the available fare classes are J9 JN9 C9 D9 Z0 ZN0 P0 PN0 PZ0 IN0 I0 O9 ON9 A5 R0 RN0 Y9 YN9 B9 M9 E9 U9 H9 HN9 Q9 V0 W0 S0 T0 L0 K0 G0 N9 XN0 X0 but the flight is 4+ months away
2. If I do book the ticket this way can I use my travel credit to pay for part of the ticket plus pay the 8k miles. Is there a better way to do this?

Thanks for any assistance!