1) all custom ROMs have built in tethering. Resurrection Remix (Nougat, Marshmallow), AOKP (Nougat, Marshmallow), Bliss POP (Marshmallow), CM 13 and CM14 unofficial... All of them. Plus the one listed below.
2) If you are a Verizon customer and need Verizon VoLTE and Wi-Fi calling, then this ROM would be best for you:
Computerfreek274_MM_1.0.4 Marshmallow 6.0.1 Stock rooted VOLte Debloated
https://forum.xda-developers.com/dr.../computerfreek274mm1-0-android-6-0-1-t3503634
It's a stock-based, debloated, tweaked version of the new Marshmallow firmware. And because it's based on Verizon firmware, it has Verizon VoLTE and Verizon Wi-Fi calling still built in. For people who are NOT Verizon customers, who couldn't care less about Verizon-only features, many of those go for other ROMs which may have more advanced CM-type options. But for you I would recommend that ROM.
3) You shouldn't be seeing that optimization on every reboot. I only see it if I manually clear caches in TWRP to force all my apps to optimize.
____________________________
CUSTOM ROMS LIST FOR ALL QUARKS
For anyone curious about what custom ROMs are available after unlocking your bootloader and rooting, go here and look at the last post.
[ROMs][Quarks][List for Moto Maxx and Droid Turbo]
https://forum.xda-developers.com/droid-turbo/development/roms-t3347701
@calsurferpunk, who maintains "unofficial" CM ROMs, started the list almost a year ago because a lot of people didn't know about the ROMs available for ALL Quarks in the
other Quark forum. (We used to be one forum, they were split in September 2015 before the XT1254 bootloader was unlocked by Sunshine.) I've tried to keep it updated. I only list the current Nougat and Marshmallow ROMs. I'm sure the half dozen custom Lollipop ROMs still work, but they are not being updated.