How safe is it to build and flash LineageOS myself? I was planning to flash LineageOS on my Asus Zenfone 2 Laser, but I recently found out it is no longer supported on my phone. However, this guide explains how to build then flash the ROM on my device (and possibly root it), and I truly want to go down this path.

What is unclear to me a this point is whether it is "safe" to do so. More specifically: 


Will I be getting security updates ? 
Will it be safe to use banking apps with the custom ROM ?
What can happen if I lose/someone steals my phone ?
Should I stick with my bloated stock ROM ?


Thank you in advance for your help !
Will I be getting security updates ?


LOS team will keep merging in Android-side security patches, so each time you sync and build you get the latest they've merged, but kernel-side ones are up to you.


Will it be safe to use banking apps with the custom ROM ?


Root is optional on LOS - if you don't opt into that, the risk is low.


What can happen if I lose/someone steals my phone ?


With encrypted data and a good enough lockscreen passcode, your data will be secure.


Should I stick with my bloated stock ROM ?


Why did you ask this question in the first place? ;)