Re: Hero System from the scratch..
6th hasn't released but my understanding is that you should be able to convert most characters forward from 5th®with minimal difficulty, in at least some cases the only significant change would be the point cost. So pretty much, once 6th is released, you can evaluate it and decide if you'd like to convert.
I can't speak to converting from Fuzion, I have the book in one of the boxes of RPG's to be shelved when I have space rather than RPG's that must be on shelves - haven't opened it in years.