The first question about the Twins infield is how many will there be - five or six? Five places appear set, Morneau, Hudson, Punto, Harris and Hardy. The question then is whether they will keep Tolbert or Casilla or neither. Complicating that decision is that Casilla is out of options, which means he can't be sent to the minor leagues without passing through waivers. It is highly unlikely that would happen. Tolber still has options, so he can be sent to the minor leagues. The other complication, is that they likely need for at least one of these guys to be able to spell Denard Span. The alternative is to have Michael Cuddyer playing center field.
One of the key questions in spring training is which JJ Hardy shows up, the emerging star of a couple years ago or the guy who was sent to the minors last season. If it looks at all likely that last year was not a fluke, the Twins are going to want a lot of flexibility in the infield. Hardy suffered on offense and , reportedly, on defense as well last year. That means Thome may get more pinch hitting opportunities and a backup shortstop may be a bigger part of the Twins plans.
The second question is how third base is split between Punto and Harris. Punto is a better defender and more flexible than Harris. If Harris is on the bench, the Twins are probably going to want a second guy who can play second base and run a little. Punto can fill those roles.
The final question is Alexi Casilla. Its not really that he needs to emerge this spring, if the Twins expected that they wouldn't have dealt for Hudson. Its whether they are ready to give up on him and/or can't find anyone willing to give them something in return. Casilla can play second and shortstop - although he has no real experience at short in the major leagues. Third base or the outfield would be wholly new experiences. It will be interesting to see if he is taking balls at those positions in spring training. If not, I suspect they are showcasing him for a trade, rather than considering him for a roster spot. They do have Harris and Punto who can play at those positions, so Casilla will likely not be a first choice in any case.
Tolbert can play second, third and short. He has played the outfield, but would need to do a lot more to get ready to play center field. But he really is the quintessential utility guy in a way Casilla isn't.
Given the decision to let Pridie go, I think the Twins are preparing to start the year with six guys in the infield. Unless they can make a trade, I think Casilla is the most likely choice with Tolbert at AAA. But there are still a lot of questions to be answered.