The Caps Lock has been replaced by the search (magnifying glass) button. If you don't use that as a search button you can remap it in settings. Go to setting under device and select keyboard settings. Click the drop down arrow to change the search button to caps lock. That's it.
My Best Buy pre-order shows a release date of 10/25 so I wouldn't expect Amazon to be much faster. That being said, I do remember Google saying that they were available. Maybe their definition of "available" is different from ours...
The Acer C720 supports legacy BIOS via Sea BIOS, so you can create a bootable USB, and then install over ChromeOS on the SSD. Vanilla 3.11.6 kernel works out of the box with the exception of the trackpad, so Linux mint will likely put you in a similar state.
By word package, I assume you mean an office suite? If so, there are two very good options I recommend. One is Google Drive. Their word processor and spreadsheets applications are basic, but very functional. Also, you can use the free web version of Microsoft Word and Excel on SkyDrive.