At my company to act as Pilot in Command, whilst the skipper takes his rest, you need an ATPL.
That means at least 1500 hrs, ATPL theory exams all passed, 100 hrs at night etc....
So:
a) normally 3 years+ shorthaul experience
b) 1500+
c) rostering not a consideration as all FO's must meet these requirements before joining the longhaul fleets
d) from day one we are trained to think/act as commanders (we are all seen as future captains) so there is no different training.
e) Command depends on many factors; experience, training record, company expansion etc.... Very roughly about 15 years.
Hope that helps a little.