Hello Krestin, You are right, there is no 15.2(3)E4 for 3750X because 15.2(3)E4 onwards is only for NG3K platforms like 3850, 3650s.  CSCux57150 is fixed in 15.2(2)E5 as well (don't think this is a downgrade from 15.2(3)E releases, it is a different...

Switch 1 will join as member because stack master n standby already exists.  Please note that priority comes into the picture during election. But if your stack already has a master/member then no further election is gonna happen when switch 1 will ...

What is the model of power supply you are using? Can you please check the below installation guide and make sure you are running a compatible power supply for 4948-E? http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst4900/4948E/installation/...

Hey Marcel, We have to configure that manually on switch and currently there is no option to download the OUI list unfortunately. Regards, Kallol