Does anyone have a breakdown of how .NET Core/4.5/MVC/etc interact, are different, etc?
.Net Standard: cross-platform comprehensive API
.Net 4.5: Windows-only build tooling + comprehensive API
.Net MVC: Windows-only web framework built on .Net 4+
Mono is another implementation of the standard.. cross-platform too, but this time compatible with the actual .NET Framework, i.e. 4.5.
So i am starting with a large and varied Win code base, i will have an easier time porting (as much of it as possible) to Mono rather than Core ?
Mono is not a strict superset of .net Core. We follow desktop more closely.
The extra APIs that are part of .net core, and are features on .net standard 1.6 will come to mono as we get the time to implement them.
Sounds like baseline API that will be present on all .Net <foo>.
ASP.NET MVC is a web framework that implements the MVC pattern, as opposed to ASP.NET Web Forms, which was control based. ASP.NET MVC versions 1-5 run on the full .NET framework.
ASP.NET Core includes MVC, and the API has stayed as close asp possible to previous versions of ASP.NET MVC. The lower level bootstrapping / hosting / middleware / config stuff is pretty different (much improved, IMO), but your application code (models, views, controllers, services, etc.) should move from ASP.NET MVC to ASP.NET Core pretty smoothly.
Controllers not so much. That's actually where the biggest changes are for most projects.
I really wish they would clean up their story. Same for UI. When to use WPF, Winforms or UWP? It's just a mess.
Any version of Core supports some version of Standard, as does any version of Framework from 4.5 on. (Framework 4.5 supports Standard 1.1, Framework 4.6.1 supports Standard 1.4 and 2.0, Framework 4.6.2 supports Standard 2.0 and 1.5, Framework vNext will support Standard 1.6 and 2.0, Core 1.0 supports Standard 1.6, Core vNext will support Standard 1.6 and 2.0, etc.)
Standard 2.0 will be a big deal, because pretty much all their active platforms will support it as of their next major version, though the earlier versions provide a handier way than has previously existing for addressing what works against the various .NET implementations, which should somewhat simplify cross-platform .NET development for the existing platforms.