Windows prebuilt binaries
What is prebuilt is the pircbotcpp-mt.dll and all of the samples against the dll. Since pircbotcpp-mt.dll is prebuilt for you in the binary releases you can and should develop new code against this one dll in both release and debug settings. Yes, both release and debug. I made the dll memory boundary safe specifically to allow this. No, it does not matter which memory model you use within Visual Studio. All will work, since I made it dll memory boundary safe.
As an example, try to rebuild the bundled console sample against it and run it in both debug and release. I provide a Visual Studio solution in the console folder for this. You do not have to download the Windows Source code to do development with pircbotcpp. You can and should use the prebuilt Binary release for developing C++ programs within Windows. The Windows source code is only provided for those wishing to see the source code, you don't need it for developing using pircbotcpp.