Can I increment both letters and numbers?

Yes. Since version 4.7.9.4 (inclusive) you can now number from A001 to Z100, by setting the values for 26 sets of 100 with ‘rolling letters’.  Multiple letters can be incremented in the same fashion.  Letters can be incremented from either the left most letter or the right most letter. For example, AAAA0001, to AAAB0001 OR AAAA0001 to BAAA0001.