You can build the portfolio for anyone you want - I think a lot of campers do it for themselves but that’s not an obligation at all (especially given the number of times you will come back to it to change it).
You can copy the design visually but not the code. That is, try to obtain the same result, don’t necessarily use the same route. Don’t copy the code ! This way you’ll already learn a lot and will be able to personalize it later.
And for your last two questions, I don’t know and it doesn’t matter because you know enough to jump in with HTML and CSS to create your portfolio.