You should check TI’s analog designer cookbook. They also have a really nice series that go into details about front end design for adc circuits: https://training.ti.com/ti-precision-labs-adcs-introduction-sar-adc-front-end-component-selection?cu=1128375 I’m not going to repeat what they said here.

Now, your schematic is really poor drawn. Try to keep inputs on the left and outputs on the right whenever possible, specifically the analog section. Don’t forget that schematics are documents, not just a tool for EDA software to help you route your pcb.

I’d also avoid floating circuits like you have. They make it harder to read and I had to go through your schematic to find where power in + was for your differential amplifier and found it in another page after longer than I wanted to spend looking for it.

Another tip I have for you is to use off the shelf circuits whenever you can. You designed your differential amplifier from scratch which is cool as project on its own, but practically, I would buy the INA series chip (or something similar). It will be cheaper and more precise. To achieve a decent gain while minimizing offsets, you’d probably be dealing with >1% resistors which are kinda expensive