Installing Paranoid Android on OnePlus 3

AGI I never had such things before. The OS is pretty stable. You can take a screenshot by holding the Power button a little until a menu pops up.
You flash the ROM first, then immediately Gapps without a Reboot in between.
I'd wipe everything again (without the data partition), then use TWRP's file browser to delete all folders on the data partition, especially "Android", but leave the zips there. Make sure to clean the dalvik cache, too. I will tak a look into TWRP to remember if I skipped a step. And you did download exactly this file: http://download.paranoidandroid.co/roms/oneplus3/pa_oneplus3-7.3.1-RELEASE-20171030-signed.zip ?

Edit: OK I'd do the advanced wipe in which you select everything except for "Internal storage". It seems the standard wipe didn't include the system partition. The go in TWRP' main menu, Advanced - File Manager and delete everything in the /sdcard directory manually, except for your Paranoid Android and Gapps files or other downloaded stuff. Then you should be able to do a proper clean install.

AGI OK if they are on a separate stick you could safely tick everything in the Advanced Wipe dialogue (except for USB-OTG of course). Just to be sure there are not leftovers of any kind anywhere. That's what I'd do in this situation.

AGI
1) yes, I still have it here if I'm correct, the file is "OnePlus3Oxygen_16_OTA_041_all_1702081756_f9fb218af59d4aa6.zip". It is Android 7.0. The previous versions were also good.
2) yes
3) Deleting the Android directory prevents Giigle's security mechanism from.kicking in, requiring you to enter your old Google account password before you can use the phone. So that's why I always delete it, to save time and to know the new OS is clean and not disturbed by any leftovers. You are right and the OS itself is not on this partition. But parts of it can read old data there.

AGI I wouldn't, but I can give you the md5sum so you can check if it's the same and then it means the bits are identical, regardless of where you downloaded from (even the most shady site):
45e55a87cfeb061319858f46ed6b6aab

No problem to install that if the phone came with Android 8.0?

Probably not, I think problems arise with new releases only due to TWRP compatibility.

Edit: OK it could be that Paranoid Android didn't work because the previously installed OxygenOS changed the device firmware somehow. But each OxygenOS comes with firmware, so they probably wouldn't have such problems ever. @degen said he had to downgrade his firmware before he could install Paranoid Android after trying the latest OxygenOS. I can imagine once you installed an older OxygenOS like this 4.0.3 version we are talking about, you would have an earlier firmware afterwards that is still compatible with Paranoid Android. Just speculation, but it could work I guess.

AGI I think I tried to move because the old OxygenOS is still vulnerable to the KRACK Wi-Fi vulnerability. I wanted to make sure I could use Wi-Fi everywhere with no worries. It is patched in the final Paranoid Android ROM.

It would be hard to fake an md5sum and the data inside the zip to still make sense. But anyways, heres sha1sum and sha256sum, too:
SHA1: 455406c0babb23668540b493c24c9221c609a412
SHA256: 4f2e5549e31ef35b41f2977e167dc50217caf83c97ad35c4f5f262e97359e0db

Impossible to fake them all at once.

AGI Did you try Oreo at all?

Yes, Oreo gave me eye strain. And @degen recently tried Pie and it gave him eye strain.

Another related anecdote...I have a Lineage 14.1 (highest it officially goes, haven't tried any XDA custom options) on a Moto G4 Play (no PWM) and in the few min at a time I ever use it it's ok. Not like a modern iPhone that can be triggering in seconds. But it's highly possible that extended use like browising etc could show it to be bad. I am not an intense phone user.

Honestly if security is your primary concern then you are not likely to find something that solves that AND eyestrain right now. iPhones are the only really secure out of the box devices, and Graphene OS (the evolution of Copperhead from it's creator) is the only android derivative I'd say is as safe, and it's Pixel only and those all have low freq PWM.

AGI

Safe is a relative term. Banking should be GENERALLY safe on a current and updated device whether iOS or Android. Anything can be hacked, but your chances go up if you use older and unmaintained software.

Most respected security experts generally seem to think that iPhones with their hardware and software security solutions are the best choice for most people. They have one narrow funnel of hardware and a single software solution so it's easier for them to control things. Android is a much more fragmented ecosystem and manufacturers use a wide variety of hardware, and implement the software in various ways...not all of those are equal.

Most custom Android ROMS are actually LESS secure than a normal, updated Android installation due to the fact they are working with older bits and pieces in the software as the manfacturers are no longer updating the device's firmware and drivers. They can be more PRIVATE by giving you more feature control and removing Google's spyware etc...but they aren't more SECURE generally. An exception is Graphene OS, which is a custom Android ROM created specifically with security in mind and only works on Pixel phones that are still receiving manufacturer support.

Thus my comment about eye safe and "as secure as possible" not being available in a phone right now. The secure phones seem to bother most of us. Personally I do banking on a computer and never on a phone. I probably wouldn't bank on a phone even if I had one of the above. I cannot say it's terribly dangerous to do it on a OP3 with Paranoid, you might never have a problem, only saying I don't feel comfortable with banking that way as it's added risk I don't see a reason to take.