I am not interested in any of the Plex Pass Features like synching etc. I just want to use Plex as the Streaming Media server for my Videos.
If I Activate (Pay $4.99) at Google Play Store for Android, Do I need to pay again to use it on Roku, or Fire TV, or iPad?
Yes, all of those are separate applications, on separate platforms, from separate stores.
That being said, I think the Roku app is free now.
And the activation is valid per ‘app store account’. If you e.g. have 3 iDevices and all of them are connected to the same iTunes account, you pay only once.
https://support.plex.tv/hc/en-us/articles/205556278-Unlocking-or-Activating-Plex-for-iOS
https://support.plex.tv/hc/en-us/articles/203868088-Unlocking-or-Activating-Plex-for-Android
