Hi Matt,
Get the 16 inch Macbook Pro. The dedicated graphics card will make a big difference when it comes to processing, which is why I suggest to upgrade it to the 8GB version (standard is 4GB). Another advantage of the 16 inch Macbook Pro is that it comes with a 6 core CPU (or you can even upgrade to 8 cores) whereas the 13 inch Macbook Pro only has a max of 4 cores.
The 13 inch Macbook Pro + the eGPU would work too, but I think it's a cleaner/more streamlined setup if you just go for the 16 inch Macbook Pro. Plus you won't get into any issues with eGPU drivers etc.
All the best.
Regards,
SAV