Closing the loop with Linuxcnc, adding encoders to Mesa FPGA?

[Desertboy]

I have the machine connected to a DDCSV at the moment but I also I have a 5i25 can I buy a 7i85S
https://mesaus.com/product/7i85s/
and then replace my 4 nema 23's with nema's and encoders to close the loop with the (AM882) drivers I have now?

Will a 7i85s and the 5i25 plus a cheap PP BOB connected to a PP for home, MPG and limits be enough to drive a standard 3 axis router?

Am I right in thinking this board+linuxcnc enable me to close the loop with standard stepper drivers as long as my Nema's have encoders?

Where can I buy encoders without Nema's?

I found on alixpress 3nm nema 23's with encoders for ~£50 each but 2 of my existing nema's have dual shafts can I buy encoders to fit on them?

They are the 4nm one CNC4you sell.