Normally draft versions you need not add to VSS, coz internally it'll maintain the Versions, if you want the document version to be match with the tool version, you add to VSS after baselining the document.
It's advisable to do review all the technical documents, it helps to find defects at the earlier stage itself.
1. What does your internal process say about controlling unreviewed, draft documents? If required, then you need to put it into VSS. If not required, then you don't. If the process doesn't specify, then ask yourself whether there is reason for putting it into source control now rather than waiting till after the review changes have been made.
2. If review is not mandatory in your organization, it should be. Formal review, especially of critical documents like a Test Plan, Business and Functional Requirements, Specifications, etc., are a best practice. As Vishnu says, they are a good way to find defects early in the development cycle.
3. Not sure of the advantage suggested by Vishnu regarding matching versions between documents and tools. Seems this would develop into a vicious cycle where modifying a component or deliverable would necessitate touching everything else associated with the project just to make the numbers match up. What's the advantage to that?