Install Safari 7 from Mountain Lion
1) No. Safari requires libraries and frameworks that will only be found in Mavericks. You can potentially snag the Safari.app from someone runnin v7 on OS X 10.9, but I'm fairly certain it will simply crash on launch due to the requirements mentioned above.

2) Yes you can still install Mavericks provided you have purchased it from the Mac App Store. It will be listed under your Purchases tab.

3) No. You will likely suffer the same discrepancies mentioned in 1) with a version mismatch.