Here is an article about how to develop for SharePoint Online(Ofiice 365):
http://www.microsoft.com/en-us/download/details.aspx?id=17069 (It's a guide for SharePoint 2010, but similar for SharePoint 2013).
For SharePoint 2013 Online with Visual Studio 2012, here are some articles about it:
Office Development in Visual Studio 11 Beta
Sign-up for an Office 365 Developer account
Get started developing apps for Office
Set up the development environment for SharePoint 2013
SharePoint 2013 Cookbook: Prepare Your Environment to Create Apps
Office Developer Training videos
Loads and loads of code samples
This forum is used for SharePoint only.
http://community.office365.com/en-us/default.aspx
Thanks,
Ivan