This Nokona X2 Elite Series (X2-1200) is actually designed for use by an adult male that is playing pitcher (for baseball). I would not recommend for fastpitch softball use. However, if you wanted a 12" mitt for middle infield as a fastpitch player, you can certainly do so. Sadly, we do not have any 12" fastpitch Nokona mitts available at this time. If you wanted a Nokona fastpitch glove at 12.25", you could look to the Nokona X2 Buckaroo Series Fastpitch Glove (X2-V1250).
The Nokona X2 Elite Series: X2-1200 features a 12.00 inch pattern and is a great size/model to consider for a teenage player who is seeking a glove for both the OF and pitcher positions. This model will allow for transition into high school as the player physically develops as it features an adult fitting wrist and finger stalls. As well, the Nokona X2 Elite Series: X2-1200 is constructed from kangaroo and stampede leathers to help the glove last for multiple seasons. This makes it a perfect fit for a year round player as kangaroo leather is one of the toughest leathers in the world.
An A2000 in the 11.5" length will be smaller than this Nokona X2 Elite Series (X2-1200) and it will be noticeably smaller. (2) Yes, you could use an A2000 in the 11.5" length at 3B if you wish (however, it will be smaller than the regularly suggested 11.75" length for 3B).