Clients clustering: How would you procede for adding other than rfm variables to kmeans?

I have my RFM clustering. I want to add:

change variables: ratio q1 to year, ratio q2 to q1, ration q3 to q2, S1 to S2...

other variables: returns of products, channel ( web, store..), buying by card or cash, navigation data on the web...

Would you do that in the same kmeans and mix with rfm variables? or on each rfm cluster do another kmeans with these variable? or a totally separate clustering since different data ( web navigation)? how to know if it is good to add the variable or not? is it bad to do many close variables like ratio q2 to q1, ration q3 to q2? how would you procede, validate...?