@mattpitts74 I purchased all second hand equipment: E-M1ii and Zuiko 100-400. I paid around $600 USD for the body. You can see
my gallery here, I have shot thousands of images with it since I acquired the setup in September of this year. I don't know what kind of photography you are interested in, but I am happy with this setup in most situations. AF is fast, the camera powers on in a second, and it is weatherproofed. I don't like the results at 400mm, so I dial it back to around 330mm. There is a gentleman on this forum who uses the full 400, so I guess it depends on your particular lens. Don't expect to get razor sharp shots every time with this much focal length. I try to steady myself with good posture or support, and I shoot in bursts in hopes to get a sharp image.
I would say its weakness is birds-in-flight. It does fine when the bird is against the sky; when against a more complex background, the bird is most often out of focus. This is the case with a lot of cameras, but this is where subject detection AI comes into play. It's too rich for me at the moment, so I make do as best I can with the gear I have. It is possible to get good BIFs; your keeper rate just won't be as high. Of the M43 bodies I know of, the OM-1, E-M1x and the G9, G9ii have animal detection. Yesterday, I was shooting northern harriers from an elevated position, and most of my shots had the background in focus. However, I got some keepers because I kept shooting.
I am still messing around with which focus setup is best for BIF; newer bodies may allow you to customize the sensor pattern. I am using 9x9, but the cross shape is worth experimenting with. Matthieu Gasquet's tests are nicely summed up
in this article, and he has recommended settings as well. I go back multiple times to cross reference his experience with mine.
In the end, every setup has limitations and workarounds. The most important thing is to keep using it and getting better at photography. Good luck!
P.S. whatever you get, make sure you UPDATE FIRMWARE!