I managed to get this to work today with the following steps (in case it helps anyone).
choco install hg -y
choco install git -y
choco install python -y
choco install microsoft-build-tools -y # One of these might not be necessary.
choco install microsoft-visual-cpp-build-tools -y
cp 'C:\Program Files (x86)\Windows Kits\10\bin\10.0.17763.0\x86\rc.exe' 'C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\bin\'
cp 'C:\Program Files (x86)\Windows Kits\10\bin\10.0.17763.0\x86\rcdll.dll' 'C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\bin\'
py -m pip install --upgrade pip setuptools
py -m pip install virtualenv
hg clone
https://bitbucket.org/blais/beancount/ Sources\Beancount
git clone
https://github.com/beancount/fava Sources\Fava
virtualenv ./.env
.\.env\Scripts\activate
cd Sources
cd Beancount
pip install python-libmagic
pip install python-magic-bin
pip install -e .
cd ..\Fava\
make
pip install -e .