I don't think it matters.
Lets play this out with assumed email addresses:
Current iCloud Account ID;
name@gmail.com, aliases: name @icloud.com,
name@me.com.
New iCloud Account:
othername@icloud.com.
Your Mac and iOS devices have been using
name@gmail.com for iCloud, and purchases in App Stores for iOS and Mac, and has an outstanding credit of $10.
You change the login to
othername@icloud.com and all purchases and credits will be available on this AppleID. Your primary email will now be
othername@icloud.com. Your .icloud and .me aliases will continue to be associated with the new ID, and you will continue to login to email for these as you do today, they are just additional reach points for your account if say, you are locked out.
If you have credits or purchases on name.icloud or name.me accounts, they are not going to be associated with the new account, just like they aren't associated with the gmail iD today.
But, if you have purchases and have Family Sharing enabled for these accounts, purchases should be available on the other "family" accounts. The only way to use credits is to login with these "name.x" accounts and buy things until it runs out.