I use my iPad more and more for email but I'm concerned about billions of emails accumulating and ending up as Gigs of backups.
Is there a way to limit the number of emails that are loaded onto iPad, then ideally tap button to load next bunch. For example, I would like to load most recent 100 then tap a button for next 100.
Also would like to limit the total amount of email on the device with last in first out.
Thanks!

Not sure if this is what you're after but Settings>Mail, Contacts, Calendars>Show allows you to select the number of emails to display in the generic email application on the iPad. I connect my iPad email to a google account that holds thousands of emails and I only see the 50 most recent.

If you need more control over your email client than the generic app provides, you might try looking at IbisMail. I haven't used it but it has received some strong recommendations on this board and in the app store.