Bringing additional existing number to you when I already have an account and number with you

I am already registered with ID mobile with an ID mobile number my wife uses.
I have the new ID sim card been delivered today & will input the PAC code Monday.

Can I leave the new sim card out the phone as I can't afford to be without phone calls for a long time? 
And then I presume I will know when the new sim card with my existing number is active, as the old sim card will stop working?

Can I then add this number (my old number with EE for 30 years) to the ID account I already have? 
As I've heard on these forums people struggle adding their existing number to an account they already have with ID mobile.

ie. I don't want to add the number that came with the SIM to the ID mobile account now do I?

Will I then see both numbers under the one account?

Will I then get two lots of £7 go out the bank on different dates?
Or can I get one whole payment out the bank for both numbers?     

As if this goes OK, I am then bringing a 3rd number to ID mobile as I have 3 numbers on one phone.
I also have two other numbers for work on Lebara, so you can see I want to cut my admin time down to a minimum. 

I'm trying to add a message & keep getting this:
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