Will the new 13 inch Macbook Pro handle running macOS and Windows in a VM simultaneously?
Yes, you can run macOS as well as Windows in VM on that computer and get a reasonably smooth experience.

Remember that "smooth" is subjective. If you're compiling the odd C# desktop app, using the debugger, etc. - that's going to work fine.

If you want to run a heavy stack with all sorts of services (SQL Servers, logging platforms, indexing systems, etc.) and have a huge project with many subcomponents - the ride isn't going to be as smooth.

The worst case scenario with 8 GB of RAM is that you're going to be using a lot of swap space. It will slow things down - but not as bad as on an old computer, as the SSD on the new MacBook Pro is quite fast.

I would recommend booting up your current development environment and check the memory usage. That would give you a good indication of whether to prioritise disk or RAM.