Galaxy clusters are useful cosmological probes and interesting astrophysical laboratories. As the cluster samples continue to grow n size, a deeper understanding of the sample characteristics and improved control of systematics becomes more crucial. For this analysis we created a new and larger ACT-DR5-based thermal Sunyaev-Zel'dovich Effect (tSZE) selected galaxy cluster catalog with improved control over sample purity and completeness. We employ the red sequence based cluster redshift and confirmation tool MCMF together with optical imaging data from the Legacy Survey DR-10 and infrared data from the WISE satellite to systematically identify true clusters from a new cluster candidate detection run on the ACT-DR5 dataset. The resulting ACT-DR5 MCMF sample contains 6,237 clusters with a residual contamination of 10.7%. This is an increase of 51% compared to the previous ACT-DR5 cluster catalog, making this new catalog the largest tSZE- selected cluster catalog to date. The zphot>1 subsample contains 703 clusters, three times more than in the previous ACT-DR5 catalog. Cross-matching the ACT-DR5 MCMF cluster catalog with a deeper tSZE sample from SPTpol 500d allows us to confirm the completeness and purity of the new ACT-DR5 MCMF sample. Cross-matching to the two largest X-ray selected cluster samples, the all-sky RASS MCMF and the western Galactic hemisphere survey eRASS1, confirms the sample purity of the RASS MCMF sample and in the case of eROSITA eRASS1 reveals that 43% of the matched clusters are designated in eRASS1 as X-ray point sources rather than groups and clusters. Cross-correlating the ACT-DR5 MCMF cluster catalog with ACT-DR6 lensing maps results in a 16.4 {sigma} detection of CMB lensing around the clusters, corresponding to the strongest signal found so far for a galaxy cluster sample. Repeating the measurement for the z>1 cluster subsample yields a significance of 4.3 {sigma}, which is the strongest CMB lensing detection in a z>1 cluster sample to date.