Q: Size limit for keynotes from iPad?

The size limit built into the iPad is extremely big.  You will hit the size limit your ISP places on each email message first.

A simple and popular way to copy files and share files amoung your devices.

https://www.dropbox.com/

Using iTures to transfer files:

http://support.apple.com/kb/HT4094?viewlocale=en_US&locale=en_US

Files Connect -- The swiss army knife of remote file connect

https://itunes.apple.com/us/app/files-connect/id404324302?mt=8

Windows File server

http://itunes.apple.com/us/app/filebrowser-access-files-on/id364738545?mt=8