Office Move - What is the best way for us?

[#1]

We currently use a PlusNet business broadband service at our current office (very happy with it) but we need to move offices in early Nov.
The new premises currently has three lines going into it.
We have an office number we want to transfer over, this is important to us.
Now from what I've read it seems moving a phone number and a broadband service at the same time can raise a number of issues and we really don't want to suffer any downtime.
Now the good news (perhaps) is we are considering a second office number on a second line. So I am wondering if the best route for us here is to get the second line installed prior to our move and start a new broadband account on that line. Then when we move get our existing number transferred and cancel out current broadband account.
Does this make sense? Are there any other issues I need to consider?

[#2]

Your best bet will be to place the broadband order on a different telephone number to that of which you are currently using.
This way, we will be able to place the order on that line as soon as it is active in the BT database.

[#3]

Thanks for the reply.
I've since learned we'll be moving exchanges so it looks like it has to be done this way.
Quick question, by setting up a date to move our broadband to the new line would there be any down time at all?

[#4]

We can place an order on the line as soon as it is active, so if you get it activated about a week before you are due to move in, we should be able to do this for you.