Pirates.com recently put up their list of 15 players here. Rob Biertempfel reports that five more players have been invited (Tony Sanchez, Andrew Lambo, Chase d"Arnaud, Brian Friday, and Eric Fryer). Adding Jose Veras and Toregas makes 22 players total.
The Pirates list Wimberly as an outfielder on the website, but I assume he'll be playing the infield as well. Biertempfel actually lists Eric Fryer as an outfielder too, but I threw him in with the catchers.
I haven't seen word on whether Veal will actually be able to pitch, but I assume the answer is no. I also haven't seen anything indicating whether guys like Atkins or Fields have opt-outs if they don't make the roster out of Spring Training.