It's always recommended to keep both ends the same. LX and SX use very different wavelengths (850nm vs 1300nm). You can normally get away with using different wavelengths if the wavelengths are fairly close to each other because receivers aren't wavelength-specific, but 450nm is a big difference so you could run into problems.
As for MTRJ connectors, they take up less space so they're preferred in some situations for that reason.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...