You could try the easy way. Use AndroidWorks instead of the TADP supplied with UE4. It is the successor to TADP. You will need to register with Nvidia to get access to AndroidWorks. But I installed it and let it download all its dependencies. Even though I have a separate android-sdk install.
AndroidWorks sets all the environment variables and integrates with visual studio. For me it was basically a one click operation to install and wait for all the huge downloads. Now Visual Studio compiles and it just works without any fiddling.
If you insist on TADP, the last time I had it working it gave me a lot of grief about environment variables. So just fix those and it should work.