Default Surveying the landscape

I'm on AT&T and considering finally upgrading my original Note to an S5. As such, I'm looking into the custom ROM scene.

I'm wondering the following:

How stable are things for the AT&T Galaxy S5 custom ROMs? Are there nice Kitkat ROMs out there that function well?

Are there any issues tethering natively with the current batch of custom firmware? What about using tethering apps?

Are there any native features of the phone that are commonly buggy with the current custom ROMs? (like the speakerphone issues on the Note?)

Does the battery take a hit with the custom ROMs?

Etc. etc. etc.