[bubblegum57]

I don't think there is one device to run everything. To have sonarr etc & kodi on one device, I think you need to build another htpc. I think qnap used to run kodi, but not anymore. You can't run linux apps on android tv. 

CE coreelec, is linux, but a cut down version, it's basically kodi, you might be able to run sonarr via kodi addons, I don't know. With CE you install it to sd card, that can then run kodi & compatible addons. You then remove the sd card & it will boot to android. 

You cannot install linux on a fire tv or shield. 

As for running out of storage, it depends on your needs. You can get 12 bay nas & 16TB hard drives. But these are expensive. A synology nas is nearly plug & play, you have packages for sonarr, etc

An advantage of a nas is the low power consumption. so a nas for storage & running the linux apps & a fire tv for playback.

As for running out of storage I meant the library metadata stored on the Fire TV Stick.. And as long as you can ssh into CE it shouldn't be a problem to install whatever you want there, even if it's not a Kodi addon. So currently I'm wondering what the best solution would be.. Also for my first question, would the ODROID be powerful enough to run some services besides Kodi?

NAS with VM running services - Fire TV with Kodi App and Netflix -> probably most expensive and traffic intense but most convenient
Android TV device dual booting with CE-Kodi and Android TV-Netflix - Storage directly attached via USB Hub -> feels hacky and could break apart easily I guess
ODROID N2+ running services and Kodi - Fire TV for Netflix -> is it powerful enough?
Custom HTPC running services and Kodi - Fire TV for Netflix -> expensive and would need intensive research on hardware, so not really preferred

For me, I don't want a hacky duel boot thing. I have multiple clients, for non-techie family that can watch tv, netflix and media all from kodi, so it needs to be easy and all in once place, hence kodi with plugins.

So for me it's a case of the best boot to kodi box, which can play netflix 4k from inside the plugin. Anyone able to confirm this on a device they have?

I don't think you will get nextflix 4k playing via a kodi plugin.

I had nextflix running on my X96 max with CE. it was so out of sync it was unwatchable. CE uses the same plugins as Kodi, because CE is a cut down linux version of Kodi.