I would like to know the following:
Is there a chance to get hired by one of the upper stated companies?
What would be the salary (after the taxes are paied) ?
What is the on/off cycle?
Would I be able to get any seniority ?
I'll take a stab for CHC in the UK....
Chance of being hired - Yes.
Salary - With that experience you'd qualify for a FO position. With those hours, about 2200 UKP per month after UK tax.
Roster - Depends on the base. Some (or one - Aberdeen) do equal time, others are different. For Aberdeen you'll probably get towards 800 hours per year. Southern North Sea somewhere around 600 per year at a guess.
Seniority - Since the unions are present and with your hours and experience, it is unlikely you'll get anything more than a "very inexeperienced FO" level on joining. There are guys coming back to the company with prior offshore experience and in many cases prior command experience - they still start as FOs.
As a side note, you should expect to fund your own JAA IR transition - it's possible a company would fund it, but it's rare enough that it wouldn't be a good idea to plan on that.
BG.