1. It Depends. If you are using Amazon Web Services, you can use their S3 service to upload/download files. The plug-in for Fire Fox works very well (as does the Elastic Fox add-in to manage your instances). Could use an FTP site. Again, if on AWS, can add FTP services to IIS or install FileZilla; open up the port (directly to your IP address) and upload. I've seen some use DropBox, but not sure if it would handle a 4GB file.
2. If using AWS, then you would RDP into your SQL Server instance and then restore as normal (like a local machine).
3. If you're going to the Web, then Application Architect is what you need to use to build your customizations and deploy to your web site. You can do the customizations locally an then save your model changes to a project bundle (in AA) and then upload just that to the cloud. Or you could use AA on the instance running in the cloud. I've done both, and there are pros/cons for each.