Panettone question

Greetings,

Long-time visitor, second-time poster.

A question (or two) regarding panettone, the answers to which I imagine are applicable to other breads.

1. I use a recipe that calls for a biga that uses 10g cake yeast of the 12g total required.  The biga is to rest until doubled, at which point the main process commences.

Question: Can I, without ruining the starter, let it sit overnight or several days so as to develop more flavor?  If so, is it best to do this in the fridge or not?

I have done many overnight rises and several day starters, but the amount of yeast called for in this recipe is what makes me wonder whether this would be a problem.  In most of the other cases in which I've done this the percentage of yeast has been much lower in the starter than what this calls for.

2. I have used the recipe before with fine results save for the fact that the final product is drier than I would like it to be, certainly not as moist as what I expect from a decent panettone. 

Question: Will hydrating the dough beyond the amount of water called for address that problem, and if so, what strategy is best employed so as to avoid excess hydration that might ruin the bread?  I've used highly hydrated doughs before, but it's never been quite clear to me how far one can deviate from the suggested recipe before completely altering the balance of the ingredients and ending up with something quite different than expected or ruining the bread (particularly in this case, given the butter, eggs, essence, etc.).

Many thanks for your thoughts,

Alan