Q: Adding devices to an existing account

Apologies for the late reply...

1. No.

2. Yes. Each Apple ID account can have up to 10 devices associated with it.

3. No. Whatever purchases you made using a specific Apple ID account will forever be linked to that account.

Since you can load all non-DRM protected purchases to any of those ten devices, in reality that has little effect on day-to-day use. The only time the original Apple ID comes to play, is when an app needs to be updated.

You can also set up Family Sharing from the main account, so others have access to files on that main account.

I am still a little confused.  I have an email that is no longer valid.  I can't delete the Icloud account email and enter the new email.  If I were to "restore" the phone and enter it with my new email, will all the apps purchased under the new email appear?

How do I add a Windows 7 device

What exactly are you wanting to do ? An iTunes account can only be authorised on a computer's iTunes (Account / Store drop-down menu), only iOS devices (iPads, iPhones, iPod Touches) and computers can be associated to an account (View and remove your associated devices in iTunes - Apple Support), and windows 7 is too old to show if you are logged into the account in iCloud on it (Check your Apple ID device list to see where you're signed in - Apple Support)