Thanks again to James and Richard:
Here is where I am up to. I have gained a better understanding of what I am doing, so am now asking the right questions.
Still some unanswered stuff, and have reduced the situation to my summary below.
Thanks for the information above- it was invaluable!
I'll check back in when I am successfully up and running with operational email!
Have had a highly educational experience of getting a more 'intimate' understanding of webhosting the last 48 hours. A bit of a baptism by fire for a Luddite like me.
All is generally well, excepting some disruption along the way.
I am learning a lot, and so becoming a better member of the wordpress community, and improving my skills at the same time.
I understand I need to enter new custom DNS records. http://en.support.wordpress.com/domain-mapping/custom-dns/
I have already updated the primary domain with the new website information (socialalchemy.com.au).
I have two questions relating to changing the wordpress nameservers and maintaining existing email for that domain name:
1.Where/how do I get the information for the custom DNS records?
2. How long do I wait before editing the DNS after entering the wordpress nameservers? (what is the best way to minimise email disruption?)
My understanding is that I take the following steps:
1. Prepare the data for the custom DNS records. (see question 1 above)
2. Enter wordpress nameservers: NS1.WORDPRESS.COM
3. Wait for propagation. (see question 2 above)
The help from everybody has been fantastic, and the forum community is working well.
Further clarification would be great in order to do this next bit with the minimum disruption to have the optimum wordpress experience.