Q1: Unless you are family sharing extra subscribed storage from #1 to #2, the two storage areas are separate. Deleting #1 will have no effect on #2.
Q2: Complicated and you need to do it the right way or else you'll not be able to use it for 6 years. Make sure you understand this:
Change your Apple Account primary email address - Apple Support
- If you remove an email address from your Apple Account, it can’t be associated with another Apple Account for 30 days for security reasons.
If you can’t change your Apple Account primary email address
- If you try to change your Apple Account to an @icloud.com email address that was created within the last 30 days, you will be asked to try again later.
- If you see a message that the email address you want to use isn’t available or is already in use, check that you or a family member aren’t already using that email address with a different Apple Account. If a family member is using that email address, remove it from their account, then try to use it.
And:
From: How to delete your Apple Account - Apple Support
“Can I use the primary email address for my deleted Apple Account to create a new Apple Account or with another existing Apple Account?
No, once your Apple Account is deleted, you can’t use the email address that you used with it to create a new Apple Account for as long as Apple retains the one-way hash of the email address. For third-party (non-Apple) domain accounts, the one-way hash is deleted after six years. For other accounts, this is retained according to Apple's retention policy, which is reviewed regularly. In addition, you can’t use that email address with another existing Apple Account except as a rescue email. Also, if your primary Apple Account email address is with a Custom Email Domain, it can never be reused to create an Apple Account after your Apple Account is deleted, even if the domain ownership changes.”
