I agree that you should use the same Emacs version. On the Mac I recommend http://emacsformacosx.com/.

I have my .emacs.d symlinked to a folder in Dropbox. So to set up on a new machine I just have to install Dropbox and make a new symlink.

This also worked for me in Ubuntu.

I was concerned when package management came in as a lot more stuff seems to get downloaded, but it just seems to look after itself.