The first thing you have to worry about is the image metadata. Whenever you take a picture, your camera adds information to the file, such as the date when it was taken, the place, etc. You must remove it. That's the first link I found on the subject if you do a better search you'll find better tools.
You must create an account on the image hosting service without giving personal information.
You must keep cookies and javascript to a minimum, because they track your activity online and reveal your browser information (screen size, computer type, browser type, etc). But must hosting sites require it on. So you can't run from it. Don't use other tools such as personal email to communicate with people - the more tools you use, the more information you give away.
You have to take care of your avatar and of the pictures you take. If you say in the forum that you live in city X and take a picture showing a city monument from a certain angle, it's guaranteed that whoever takes the trouble to search your posts will find out who you are and where you live.
Like you said, VPN is important because it masks your IP. You should always check for leaks before you start to brownse.
I suggest you read this link: https://www.privacytools.io/ it provides a nice education on the subject.
In that case, why do Threema themselves claim that Google Play Services are required? The most likely explanation to why Threema works on Blackphone is that Blackphone's proprietary operating system (Silent OS) includes a built-in alternative to GCM. At this point, open-source operating systems like Paranoid Android and CyanogenMod don't include built-in alternatives to GCM, even though there are FLOSS projects like GmsCore.
Ok, my understanding was that I would route all my traffic to the PiVPN to make use of the PiHole add blocking, the Pi would then send my request off to a server provided by Trust.Zone which would hide me from preying eyes.
And the journey back would be the same but reverse Trust.Zone server > Pi > Mobile
Are you saying that the above idea does not work?
Thanks.