Domain Mapping Question

Our goal is to map domain.com to it perspective subdomain.com counterpart and hide the subdomain paths. We want to, however, to still be able to offer standard email accounts to our clients as well.

The variables in this test are:

• We have multiple authoritative NS.
• We are using CPANEL and WHM.
• The test domains are at godaddy.com

Here is what we've done to accomplish our goal: We've changed the NS on the test domains to the authoritative NS, then created each test account in WHM. We then jumped into EDIT DNS for each domain and made sure the NS was the NS that are being used for the account and saved the edits. (in other words the default NS that is assigned is the older company. We changed it to reflect the NS that matched the site that has WMPU.)

We then looked at the A Records and there are many. There is a "root" A record and then one for FTP, CPANEL, WEBDISK, WHM, WEBMAIL, etc.

The questions are: if we want to give or clients email but have the site run off the subdomain:

1) Is this a good way to do it?
2) Do we change all A Records or just the "root" A Record?
3) If this is a bad way to do it, then how can we setup domain level emails?
4) We change the a records on the test account, not the account that has the WPMU, right?
5) We didn't use advance DNS since we were changing the A records, but just went to DNS editor in WHM. Was that okay?

Everything is still propagating, so we have a day or so before we pull any triggers. Thanks for any insight.