What I dont like about the a7II its the lack of usb-c and I'm not sure It can charge via USB. I tried for One month the a7 and It was very slow, I Hope a7II its a bit faster. I was thinking also about a7rII, only a bit worried about the Weight of the file.
If you can only afford $700 for a used A7II it will take nice photos, when they are in focus, when the battery still has juice in it, when you're not waiting for the buffer to clear, etc.
Based on the OP's original post I don't think this will be an issue. They aren't planning on shooting action so AF will be fine. This can also impact battery consumption. I've not had issues with batteries always running flat. If you're not shooting bursts the buffer also isn't an issue in my experience. Yes newer models offer more but more isn't always needed.
There is more to AF performance than tracking. Reliability and accuracy was a problem for me when I used the A7II. It's a camera that struggles to AF in moderately challenging situations, ie: backlighting, low light, etc.
Battery life on the A7II is objectively poor by today's standards. However, if you don't mind carrying 2 spares with you when you're going to be shooting all day that's fine. But the III series bodies with the Z battery are a lot better. Again, you don't have to be shooting sports for this to matter.
You get locked out of many functions when the buffer is clearing on the A7II. So, even if you're not shooting a 30 frame burst, it can be an operationally frustrating camera to use.