Question

is there any lower limit to the electric force between two particles placed at a separation of 1 centimetre​

Answer 1

Yes, zero

But if you want a finite answer remember that charge is quantised, so least possible charge is e

Hence least possible force is (ke^2)/(10^-4)

Which is 2.30708 * 10^-24 N

Answer 2

Yes, it is zero centimeters