1) As I understand it, it would be great if it could be a part of the main development project - do you think that would be realistic? It would require to make a few changes to the source code, for example some invocations of the IMPLEMENT_SERIALIZE doesn't compile with msvc, and also some other minor things. But the code should certainly be able to be modified to compile in both mingw/linux/msvc. Because as I understand it, you are now basically maintaining separate modified sources for this to work.

2) Would you consider to move all 3rd party libraries into your project? I tried it just today, and for example openssl and boost libraries can be comfortably added to the MSVC project through the NuGet Manager - no need to download, install, and compile them separately. Also the berkeley-db, it's just a bunch of headers and libs, it could be added directly to the project. Also the QT is doable, since we use it at my work, and we just integrated the sources to our source code tree and compile it together with our files. This way, people could just download the msvc solution and it would work out of the box without the need to install anything else.

3) Debugging: Please, did you manage to debug with Visual Studio? My problem is, that the blockchain is being downloaded (using the debug version of the bitcoinqt from your project), but at certain point, there are some nonstandard transactions there, which are handled by try/catch block - there are some invalid indexes to std::vector, which causes exceptions, and those are properly handled by the catch(...). But, every time this exception occurs, the exception dialog box is invoked in Visual Studio, and I must click "Continue"...but this happens hundreds of times, making the debugging practically impossible. I just didn't find any way how to permanently suppress those dialogs (so the breakpoint will not be invoked when handled exception occurs).