There is no roster pattern, and certainly not any sort of 4/3 or regular arrangement. As a junior guy you can expect to do a predominantly 3, 4 or 5 day early tours, which can be consecutive, mostly over the weekends.
Holiday entitlement is 4 weeks leave per year and 2 weeks duty free week (you can work in the DFW if you so choose), with half of each in each season (winter/summer). Leave and DFW is bid for seperately each year and each calendar week attracts a number of points according to its popularity. It's allocated on in points order to the people with most points. As a newbie I think you enter with mid-table points. There should be a reasonable chance of getting the weeks you want (unless its Xmas) but bear in mind the popular weeks attract only a single point as opposed to five for the unpopulars, so by bidding for low point weeks you ultimately reduce your bidding power for next year. Also if you don't get leave over Xmas then there's a good chance you'll be working it this year.