Panning vocals left and inserting a compressor is a terrible idea!
Buy 2x 2 channel units or a 4 channel comp. dbx 1046, presonus makes an 8 and 4 ch comp too.
Compress no more than 3-4 db, ratio at 2-2.5, output at 0 to +6 max, use the RMS or over easy setting. Set up your knobs then bring...