PaulS:
Can C++ do everything C can within Arduino without any limitations?
No, of course not. There is no standard in, no standard out, no operating system, no file system. So, none of the C or C++ functions/classes that deal with those items are going to work worth a damn.
What I mean by this is: If I use C++, is there anything that I won't be able to do that someone using C could.