> So with c# 7 all I need is VS 2017?
All you really need is the new C# compiler. You can get that with VS2017, or standalone. But the programs produced by this compiler should be runnable on pretty much every runtime out there.
> It'll work with existing .net 4.5.x and 4.6.x projects?
Definitely.
> I tried tuples and VS complained
What was the complaint? in order to use Tuples, you need a reference to add the System.ValueTuple NuGet package as that's the type under-the-hood that packages up the tuple values so other people can consume them.
This is a nice approach because it means your APIs can use Tuples, while people using C# 6.0 and earlier can still use them. effectively.
> In order to compile on a build server do I need an updated toolchain?
If you use C# 7.0 features, then use. You always need the appropriate compiler to use the latest language features. But you shouldn't need to really 'upgrade' anything else if you don't want to. (You can, of course, if you do want to).
