Our team (5-10 developers) plans to adopt Subversion for our .NET (Visual Studio) projects/solutions (VisualSVN Server, TortoiseSVN / VisualSVN).
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We use one big repository, and just have everything structured in subfolders (/project1, /project2 etc) and that seems to work fine.
The Apache project has a huge svn repository and it seems to do OK for them! :)
In terms of organisation, the structure you gave looks quite reasonable. I think anything goes, pretty much, so long as it's rational (i.e. mixing up every single tool with every single project is probably a bad idea etc). So pick something which works for you (tools/, projects/ etc). Subversion has pretty good support for moving things around in the repository, too, so you can always change if necessary.