My iPhone 4S allows retrieval of 1000 emails. If I backup to iCloud,will I have access to greater than a 1,000?

The iPhone allows retrieval of more than 1000 emails. That is the "Show" recent messages setting for a selected mailbox - to show the 1000 most recent. If a mailbox has more than 1000 messages, there is a Load More Messages selection at the bottom of the 1000th most recent message.

iCloud doesn't backup email. An iCloud email account is accessed as an IMAP account and the same setting on iOS devices applies regardless the email account type.