Great job overall! 
The exterior looks realistic and believable as a physical setting from afar.
I can see lots of attention to detail in the interior as well, which is key in selling the believability of a 3D space (even if the overall style isn’t necessarily PBR.) Something you may want to do is add more surface imperfections to your materials, which will add a whole other level of detail. (However, since you said your characters are going to be toonish, this may potentially end up making the characters look out-of-place. Just something to keep in mind. 
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While it’s commendable that you took the time and effort to make almost everything in the inside of the diner, I’d recommend not doing that for future projects. 
If you’re intending to make an entire animated short as a one-woman production team (at least for now) you’ll need to save as much time as you can in different areas. Just animating the characters could potentially take a couple weeks or months on its own, and adding an extra 2 months for creating the environment means you’re potentially stuck for 4 months on a single project. That’s a lot of time, especially if you’re just learning animation. If animation is your focus right now, then focus on the animation; the environment itself can be built using assets found online, saving you time in that department. (Just as an example, for my last 2 or 3 personal animation projects, I reused the same hallway I modeled and textured in an hour just so I could get right to animating the cameras and characters. This definitely saved me time, but animating Resident Evil: Covenant still took me 2 whole weeks to do. And the character animation here isn’t even that crazy or detailed)