A low minimum inhibitory concentration does not by itself establish that an antibacterial hit is suitable for progression. This study integrates bactericidal, kinetic, biofilm, mammalian-cell and membrane-oriented data for SJ-7, the leading member of a ten-compound thiazole-Schiff base hybrid series. SJ-7 showed MIC values of 2 µg/mL against methicillin-resistant Staphylococcus aureus (MRSA), 4 µg/mL against vancomycin-resistant Enterococcus faecium (VRE), 16 µg/mL against multidrug-resistant Escherichia coli and KPC-producing Klebsiella pneumoniae, and 64 µg/mL against multidrug-resistant Pseudomonas aeruginosa. Its MBC was two-fold above the MIC for all five organisms. At 24 h, viable counts against MRSA declined by 2.10, 4.00 and 5.20 log10 CFU/mL at 1×, 2× and 4× MIC, respectively; corresponding VRE reductions were 1.78, 3.40 and 4.50 log10 CFU/mL. In an MRSA biofilm assay, SJ-7 produced 67.5% biomass inhibition at 2× MIC, exceeding SJ-4 and SJ-9. HEK-293 testing gave a CC50 of 164 µg/mL and preliminary selectivity indices of 82 against MRSA and 41 against VRE. Membrane-oriented measurements increased with concentration, reaching 360 RFU permeability and 80% depolarisation at 4× MIC. Collectively, the data support SJ-7 as the strongest progression candidate in the series and are consistent with a membrane-perturbation component to its phenotype.