Where to place a MOSFET switch
Most coin cells have very low current specifications, both for charging and discharging. For discharging, this means you have to switch off wifi or your supply voltage will drop dramatically (basically to zero). For charging this means you can only charge very slowly.

If you want to "fast" charge your coin cell, ie with more than 10mA, you severely degrade the number of cycles. I once did some measurement with some Maxell LiMnO2 cells (IIRC CR2032) and didn't get more than 10-20 cycles out of them.

I suggest you use something else than a coin cell.