@jonwayne Treating the space would provide an overall improvement. Also, a different mic, perhaps a hyper-cardioid (Shure Beta 58A or a Sennheiser 416) would help with the room noise.
Background vocals tend to sound best with ultra-heavy compression amounts. Best to apply more compression to the backgrounds and less to the lead vocals. EQing lows out of background vocals helps. Recommended compressor types: VCA, FET.
Background Vocals
Attack: Fast, 30-50 ms
Release: Slow, 200-400 ms
Ratio: 4:1 to 8:1
Gain Reduction: Heavy, 4 to 10 dB
EQ pre-comp: HPF 100 Hz, -24 dB/oct.
A good place to start with pop vocals is a 5:1 ratio. Try a higher ratio for a more controlled sound or a lower ratio for a more natural sound. Gain reduction is usually heavy for a properly treated pop vocal. Recommended compressor types: Optical, FET.
Lead Vocals (Pop)
Attack: Fast, 10-20 ms
Release: Medium, 150-250 ms
Ratio: 2:1 to 8:1
Gain Reduction: Heavy, 2 to 5 dB
EQ pre-comp: HPF 120 Hz, -18 dB/oct.
Aside from compression, a properly-dialed high-pass filter (EQ) can produce a significant improvement in vocal recordings. In particular, a great many podcasts could sound infinitely better with a simple high-pass filter at 150 Hz, -12 dB/octave.