Target AFR

While tuning with a narrowband O2 sensor. Would you advise changing the target AFR from 14.7:1 to say 14.3:1 for E10? Also would this change be done before or after MAF calibration?

I probably need a little more info to really answer this accurately as it depends on the specific ECU. Technically the stoichiometric AFR 'should' accurately represent the stoich value of the fuel you're using however in reality for E10 this is seldom done since the effect of 10% ethanol is relatively minor and the closed loop correction can pick up the relatively small errors.

If you are going to change this then it must be done prior to scaling your MAF as both will affect the final fuel delivery.