Leo,
Printed gears are quite adequate for this particular purpose (and many other).. and I am perfectly happy with their performance as part of this focuser (where there are no heavy loads - remember, this is plastics.. and printing is not as good as molding ).
Of course, when in doubt, the best approach is to try and see for yourself ;-)
As to encoder as additional input to focuser controller, I used
similar to this one from ebay. It is incremental and I use it very occasionally (mostly I focus via USB).. More often, when I need to focus my C11 between presence of FR and native FL, I simply disengage the gears (by rotation motor bracket) and focus manually (as designed by Celestron).