The Trial watermark is expected behviour if you work with the Trial key and your own app. The SDK sample app doesn't show a watermark, so this would be the best way to start testing.
To your questions:
1. You can find the hardware requirements for Android on this page. As we offer own solution as well which can be e.g. used as fallback for devices that don't support ARCore, our supported devices based is much broader.
2. Yes you can work directly with the sample app and change the code / content directly in the sample app.
3. Yes once you publish your app, you'll need to have a commercial SDK license.
I made a project of instant tracking using wikitude, it works fine on unity test environment but when i build APK for android and runs it on my phone, it show Trail text all along the screen instead of showing camera as shown in the picture
i'm using Wikitude-unity 8 and Unity 2018.3.5f1 (64-bit)
Any idea why its showing Trail on screen of my phone while it works perfectly fine on Unity test Environment
i install it on my friends phone ( samsung A3 (2017) which support Arcore ) but still now working on that phone too