R5 is not a critical value. It determines the input impedance looking into the EQU input and might be conveniently set to 10K ohms. You can use any value in the range of 1K to 100K.
R10 is ten times the value of R9 according to the text. That seems awfully high to me and I'm not sure why they do that as it appears this resistor is simply the input R for the mixer (depending on the value of R12 which I don't quite understand).
The final stage is a simple audio summer (audio mixer) whose gain is set by the value of R11. I don't know how much level you want, but a good starting point might be to set it to equal the value of R10.