New to macbookpro, have created so many passwords can I consolidate them to just one ?

I use the password manager called LastPass

For your ISP change:

I no longer have an email address that was also my Apple ID. Can I still use the email address as my Apple ID?

Apple recommends you change your Apple ID to your current, working email address. This will not create another Apple ID, it will only change it to your working email address. See Changing the name you use for your Apple ID if you'd like more information.

You really can't start again unless yo want to create a new Apple ID. However, purchases a locked to the ID that originally purchased them.

Your Apple ID and PW should be the same as your iCloud ID and PW

You can reset your KeyChain by:

Resetting your keychain in Mac OS X - Apple Support

It does not resolve your ISP problem.

There are easy to use password managers in addition to Keychain to help store and 'remember' those IDs and passwords (and other details, security notes, etc) so that whether on phone, tablet, desktop or laptop you should be able to use one program across all of them.

I use to rely on a spreadsheet for serial numbers, program versions, contact info, and later added login details.

Using one password for everything is not a good idea, if someone were to get the "master key" they would have access to everything.

Watch out for fake emails saying you need to do something, "spear phishing" is the easiest way for someone to hack or steal your credentials.

Keychain is another built-in thing about Macs that is "insanely great", but they never seem to explain it properly to make it accessible.

This article does some of that explaining. By default, your primary Keychain is a locked place that opens automatically when you log in and is ready to automatically store and retrieve most of your other passwords. It is hard to explain, dead easy to use.

http://www.macworld.com/article/2013756/how-to-manage-passwords-with-keychain-ac cess.html