Default Some questions before buying one

I have a few questions before buying the D802 version:
- how is the flashing of custom roms process ? Does G2 have locked bootloaders ? Am I risking warranty void if I flash custom ROMs ? By risk I mean, can I revert to stock without the service to know that I flashed a custom ROM/rooted it ?
- how does the back feel? Is it slippery ? My main concern is that it will be incommode to use it since looks really shiny in reviews...
- how are AOSP roms comming alone ? CM? Are they good enough for daily use ? Does KnockOn work on AOSP ?
- does the screen have any problems like backlight bleeding or dead pixels ? I see on Nexus5 thread a lot of this issues and well.... n5 is made by lg also
- is the wifi connectivity good ?

Please provide me with any weak spots of the device... negative issues about it.