Here is an explanation how to install the stock OS manually. This will wipe your phone so backup first. I leave it up to you if you find this easy or not.
About your bonus questions:
I am very happy with LOS and I just did a comparison of stock OS and LOS. I reverted back to LOS because the stock OS is in my experience not working better and there are certain features in LO plus the TWRP recovery system that I really appreciate. Just to be clear I am only talking about the FP2 here. My Galaxy Tab S2 tablet in comparison shows very bad GPS performance on LO compared to it’s stock OS.
And yes - it is stable.
If you have a relatively new FP2 (screen) then be aware that old versions of FP OS (which you’ll need to go to first before upgrading to the latest version) will not work with the screen. Here is another way to go back if you prefer recovery over fastboot.
My battery life is great.
Here is a screenshot. Note that I use Battery Charge Limit. That’s why the battery never gets above 80%.
Do the following : before installing LOS, use the fastboot tool to flash TWRP, and within TWRP make a full backup of your current OS (excluding photos and external storage) to a SDcard.
Then after installing LOS you can easily revert back to your previous OS !
Yes I am LOS is my daily driver since the unofficial porting !