Neveragain
Welcome to civilian life! All of what you need is in the public domain, much of it here on Pprune, although some of it will cost you a bit of money here and there.
Who operates what from where?
Your best bet for this info is Flight International's annual airline survey. I'm sure this would be available as back issues (it's spread over three issues, I think). It also gives addresses and contact numbers for each airline's HQ. More background information can be gained from 'Airliners Monthly'. It's abit of a spotter's mag, but full of useful info.
Range and payload (type specific)
Not sure why you'd need great detail on this, but your best bet is the relevant manufacturer's website.
Rostering and contractural info AND Company policies and conditions
This sort of info is best obtained from the unions if you don't have any internal informants. IPA or balpa in UK, IFALPA will probably be able to give you contacts for foreign airlines. If an airline is hiring, the basic info should be on their website, but it's always best to get the warts-and-all view from a current employee.
Trends and forecasts within the industry
Your best source for a variety of opinions is here on Pprune, but you do need to be able to sift the dross from the useful info. Flight also, despite its detractors, has pretty reasonable insight into the industry. The broadsheet business pages will give you a view of the industry from the financial perspective. There are a number of other websites which may or may not be helpful - I'm sure others can supply some URLs.
top tips for interview research material
Check out Transair Pilot Shop for a variety of useful interview preparation books. One of the best is the Cathay Interview book, although most airlines don't recap the ATPLs in quite the way Cathay does! (Believe me, I've done it!). There've been a number of topics here on CVs and interview techniques which it'd be worth your while searching for. I have to say that it might pay to research with a view to your target airline, as each airline's interview and selection style is quite different. When I left the RAF, I completed the selection procedure for Cathay (ASL), BA and Virgin. They couldn't have been more different! None is as intimidating as the RAF's selection procedure, though, so don't get too worried about it!
If I can be of any more help, e-mail me.