Questions on converting from tanked gas to mains gas

I called Bord Gais and they told me that they can connect me to the mains for €250. The existing system is a Calor gas tank out the back. I do not have a contract with Calor as I've just bought the house. As far as I'm aware the existing boiler can be converted to use with the mains supply.

If anyone can answer any of the following questions for me, I'd greatly appreciate it.

1 - Do I need to call Calor to tell them that I'm switching from them, and ask them to come and collect their tank? Will I be in trouble with them if I just plough ahead without them?

2 - How much roughly would it cost to convert the existing boiler and have a gas installer complete the necessary piping etc?

3 - How much extra would it cost to get a new boiler rather than converting the existing one?

4 - Can anyone recommend any gas installers in Cork City who could do the job for a reasonable price?