Translation:The period goes from October to December.
I wrote "The period lasts from October to December" and it was wrong - is this unacceptable?
Period's would normally be assumed to be a possessive form in written English, not a contraction of "period is." "The period's duration is one hour." In spoken English, I have heard something like "The period's too long." but it would be unlikely to be acceptable in written English.
he\she\it all use the same conjugation, so here va means IT goes; IT is the period, so "the period goes"
"Il periodo va..." might be translated in English as either "The period runs..." or "The period lasts..."; as far as I am aware, we do not say "The period goes...". [UK Native speaker]
'fra' is actually 'between' so contextually that would work, unfortunately it's not the exact translation though!
Because dicembre doesn't start with a vowel, so doesn't need 'ad' to sound better and distinguish it from the 'a'. For a more detailed description of this, see http://italian.about.com/od/grammar/a/aa091708a.htm