[daydr3amer]

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

You can add an external usb stick to gain extra storage for the fire stick. Troypoint is a thing to google, but it comes with a lot of other crap trying to get you to buy a vpn. You need an OTG cable & usb stick.
I don't know if the Odroid would be powerful enough, you could ask at the CE forum. although it is the most powerful amlogic device at this time. 

Android TV device dual booting with CE-Kodi and Android TV-Netflix,  these android devices do not include single board computers like the Odroid or N2 they don't have android. EG X96 Max + the android from these devices won't run 4K netflix as they are not certified.

Hmm, and the affordable NASes come with 1GB RAM only. Additionally the VM would need access to the USB port for the tvheadend tv card, and I don't know if thats even possible.. Seems like custom is still the way to go