Questions about MS Visual C/C++ Redistributable Versions/Overlap

These are questions I've been stuck on for quite a while and haven't been able to find a good answer on around the net. I've done many searches but haven't gotten the best idea of this, so if anyone could offer their insight I'd really appreciate it!

So yeah, I know that there are various different versions of MS Visual C/C++ required for programs to run (i.e. 2005, 2008, SP1, x86, x64). I've noticed with various application (and game) installs, they forcibly install this on your system even if you apparently have your own version of it already. Here are my questions:

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1.) Does it really matter what version you have? I'd think higher versions would be backwards compatible, or am I wrong?

2.) Do these overlap? Or do they coexist without any problems?

3.) Does it cause any damage/detrimental effects having too many of these? (slow-downs, etc.)

4.) If I were to uninstall a similarly named version (i.e. uninstalling 2008 version 9.1.1 when I have 2008 version 9.1.2 as well) would it mess anything up with the other version?

5.) I'm running a x64 OS and these installs bombard me with x86 versions. I haven't had any issues, but is it recommended to use the x64 over the x86 given the OS? Does it really matter/effect programs? Or is this just a preference thing?

6.) This seems to apply to .NET Framework versions too, are the answers the same for this department or are they different? (if they do differ, if possible I'd like to hear the answers as well).

7.) A bit off-topic but for certain game applications, they do a similar thing with DirectX 9 updates. I'm running DirectX 11 and I'd think it'd be backwards compatible (not too well versed in this area though). Are multiple installs of DirectX 9 updates detrimental at all or benign? Is there even a way to remove it when there's say 3 games that all install DirectX9 updates one over the other?
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And that's all I can think of at the moment. It might be asking for a bit much but again, if anyone can help I'd be grateful!