Hi Nitin,
Hope all good.To answer your questions, most depend on how you are willing to pay & what kind of a lifestyle you have.
For the Cost of living if you are not looking for a super luxury place I would say 25-30K(RENT)+another 30K as the living expenses.If you want more detailes check out Numbeo
IT field is Kind of Saturated in Colombo (I'm not sure what kind of vacancies are there for º£½ÇÂÒÂ×s,But I think most of them hire locals)
For luxury living I would say you will need around 75K-100K to rent a nice house
This is highly dependent on how far you go,where you stay,what you eat etc etc.Normally for a day rental It will cost you around 10K for transport & 20K-25K for accommodation.Food is cheap in Sri Lanka & I think you can manage