1. If by advanced menu, you mean the Status Toolbar, then no that is not an option, though you do have the option of hiding it from view altogether.
3. Container options have expanded significantly with Filemaker 12. A container field object can now be "optimized" for interactive use and thus you can insert a PDF into the field and be able to flip through the pages right in the container field.
And external storage has been added as an option to simplify issues with container fields when used over a network. With external storage specified, the files are stored in an external folder.
4. FileMaker 13 gives us the option to perform scripts on the server (as though a server schedule performed the script, but now it can be initiated from a client). It's not a panacea--there are a lot of limitations, but it's more than we had before. And some comments from FileMaker suggest that an increasing number tasks are being perfomed "server side" but I don't have any specifics on that.
But there are ways to put some limits in place--keeping your found sets small being one of them, that you can do with your current versions or in the latest version.
And FileMaker 12 had a lot of issues with slowed responsiveness--mostly corrected now.
5. You'd have to ask a sales manager. As far as I know, those design options are still there.
If by "backward compatible" you mean that FileMaker 12/13 can't open past versions without converting them, I suspect that they really didn't have much choice if they wanted to add the new features that they added. Once upon a time, each new version, from 2.5 to 3 to 4 to 5 to 6 was a new file format. Then they released 7 and managed to keep the file format unchanged for versions 7-11 before the change to 12 required a new file format.