Does rim size make a difference to chain length?
The rim diameter of the wheels has nothing to do with the required length of the chain on a derailleur equipped bike.

That does make a difference is the size of the chainrings and cassette sprockets. If you are using the same cassette on both the 660b and 700c wheels then the chain length will not need to be changed.

You dont say when in this process you are switching from 1x7 to 1x10. You will of course need a new 10 speed specific chain when you upgrade to 1x10.