I'm planning on building a program that will carry out HPC. I'm aware that C/C++ is significantly better than Python in terms of the speed of computation. However, I'm not yet proficient in C/C++, so do you think it'll be wise to build a fully functioning prototype of sorts in Python and then get it rewritten in C/C++ by others/me in the future.
It is probably a good idea to stick with Python if you have expertise with that. I am assuming that this means you are using numpy/scipy. Depending on what you exactly want to do, well-written numpy/scipy code can be very fast and even comparable to C performance.
If you really need the extra speed of C, you can use Cython so that you keep the majority of the code in Python and write only the bottleneck in C.
Python can be used for HPC with no problem. Most computation intensive work will be done with libraries written in C/C++ such as Numpy/Scipy. You can write your key algorithm in C/C++ also. Even if you want to write algorithms in python, there are plenty of methods to gain comparable performance to C/C++. Cython compiles program written with python-like syntax to C; Numba compiles your key algorithms (a python function for example) to C when needed.
HPC is not only about performance on a single computer, you have the choice to use cluster or GPUs to further enhance the computation performance. Python is good at that also.