My story. Tried flashing Black Pearl ROM using Philz Touch. I already wiped and didn't backup the old ROM. Then turned out i can't flash because the Black Pearl wipe script is not up to date and won't work with Philz. In the end, i end up buying a USB OTG cable, copy TWRP on it and flash it. Then i can flash Black Pearl ROM.
It doesn't end there. After flashing the ROM, tried restoring Titanium Backup but it got stuck at Poweramp. Rebooted and it got stuck at Android Upgrading. Took me a while to get back to Recovery. So i cleared data. Now it ask to flash OTA update. So i pressed install update. Turns out to be a big mistake. Now it's stuck in Recovery boot loop. Luckily there's a solution for that on XDA and now i'm back on Dirty Unicorn.
But i think the Black Pearl dev probably fixed this problem already.
Hopefully some of that feature will be available on G2. Else i guess someone will definitely port it.
If you're flashing a different kernel then yes, after flashing the ROM then the kernel. Else just use whatever that comes with the ROM.
I read that some guy got 10 hours SOT on XDA. No idea how long can you get on the G2 with your setup. Have you tried? Didn't bother to UV and UC yet.
I dont see why it cannot be port. S800 is capable of doing that.