Tier2 CoS years of stay

[ganygan]

Hey Guys,
My company is providing sponsorship for 1.5 years in first instance and they say they can renew it up to its full term(3 years) in second instance.
As far as I understand from UKBA guidance, the same CoS cannot be renewed more than once. Which means I can work with the current company only for a maximum of 4.5 years.

Could you please help me with the following concerns?

1) Can I switch to a new company and get a new CoS within the next year or so and allowed to get full 3years in first and get it extended as well?
2) Can I move to a new company and get a new CoS after 4.5 years, and get only for 6 months so that I will complete 5 years and be eligible or ILR?
3) Should I have to take a cooling off break period of 12 months after 4.5 years?

Please help me guys..