Commissioning and crew assignments

This shouldn't be too difficult for all you navy guys out there. :)

When is a Captain assigned to a ship during commissioning/construction? Does that happen only when its time for the shakedown cruise or sometime before?
Would there be any major difference for a new class-ship, i.e. the first one of a new class compared to a new ship of an older class?

What about the crew? How many of the permanent crew will be assigned to a ship during shakedown and/or construction and how many will be added later once the shakedown is over and the ship is assigned to regular duties?

Depends. I would say most are assigned about the time of the trials, with some of the plank crew on board for trials and shakedown. Some ships -- I would think class prototypes, especially, will be under the command of a construction leader during trials, with the plank commander aboard as an observer to learn the new ship.

They would probably fill the lower ranks after the construction is complete with final crew replacements etc. at the time of shakedown.

Figure most of the crew would rotate in and out of the ship as per 'needs of Starfleet' or when possible. Deep range missions that last 10 years would probably have the same crew aboard for a tour, with a change out after that.

But it's your campaign, man -- do it your way.