I think a comfortable distance between the island and the counter is around 42". It seems that you have only 30" between your cook top and the counter. I might be a little too tight. The wall between the entrance and the kitchen could be 4' long instead of 6', you would then be able to move the island a foot which would give you more room between the cook top and the island. Could you switch the location of the toilet and vanity in your dad's bathroom so your enter facing a vanity instead of a toilet which is a lot nicer.

Most my doors were already here, but I did have one moved over, about 6 inches. However, the entire space was demo'd, and rebuilt, so that's not the best example to draw from. If you want the door hidden, in a pocket, yes, you will need a skilled carpenter. Essentially, the opening header and frame, will become twice it's size, with the "pocket" part, hidden behind the wall. The studs/supports will need to be removed to make a space for the door to slide into. Do you have any switches or outlets on the fireplace wall?

cool --but you can see the entire floor has been raised--do you have the ceiling height? a closet 'step up' would be less of a structural commitment, OR a buildup under builtin furniture--like bookcases flanking a fireplace, also some great ideas on HOUZZ i'd never have thought of. sorry i'm not tech-ie enough to paste the site:) of course if you go 'structural' --all walls and ceilings are fair game as well. remember that ease of access [or lack thereof] can affect stealth mode greatly--as in your pic: every time you step onto the 'box' in your pic you would hear a 'different' sound.

Is there already a chimney in place? The space looks very small, so consider a thin stone veneer and a small, electric fireplace for the look without the need for major construction. See Houzz photos under "electric fireplace" for ideas of style, incorporating storage.