If your buddy thinks you will have problems over-heating a 300 2T, you will most definitely over-heat a 4t. It is much cheaper to maintain a 2T woods bike than a 4T woods bike. Modern KTMs can be set up to have almost no 2T hit or a big hit.
My daughter's 1st big bike was a 200XCW and she did great with it.
If you have a line on a well set up KTM 300, I would be on it. Make sure the jetting is correct (JD Jet kit is the way to go), then ride it and have a shit ton of fun.
all around good guy