Tier 2 is basically same as Tier 1. Just prefix agk:: before using any of the AppGameKit api. Of course the normal differences... semicolons at the end of statements, typename first when declaring variables, etc.
I use VS2015 Community and everything works fine. In my current game project I was building it in both AppGameKit BASIC and a C version at the same time. But I'm dropping C version going forward because this is kind of a little game jam type event with some folks on the Unity forums. So is a bit silly to spend time porting code in this scenario.
But I do plan on making at least one simple game in both BASIC and C versions (and maybe do a third port to C++ oop too) and release the source here at some point. Just because I think it would be quite helpful to many people to see the same exact game done in both AppGameKit BASIC and C & AppGameKit library.
TI/994a (BASIC) -> C64 (BASIC/PASCAL/ASM/Others) -> Amiga (AMOS/BLITZ/ASM/C/Gamesmith) -> DOS (C/C++/Allegro) -> Windows (C++/C#/Monkey X/GL Basic/Unity/Others)