Dev environment for legacy Visual Studio code?
... legacy projects that all require different versions of visual studio ... 


Don't you just love Visual Studio?


  ... I want to set up the projects such that it doesn't matter which visual studio the project is opened ... 


If your "legacy" goes back beyond .Net 2, then you're out of luck. 

New, shiny versions of Visual Studio won't open .Net 1.* projects and will shrink away in horror from anything that needs anything created in 'Studio 6 (except, possibly, C++, the one language that's survived .Net-ification largely unscathed).  

Most of the newer stuff will happily co-exist, but you'll probably need to think about  containerising the earlier stuff.