We lived in a 12x60 mobile home for many years.

Looking at your plan I would suggest that you reduce to one bathroom, especially since the full bath is not an ensuite. Your occasional guests don't mind if there is a shower in the room where they take care of business, and with only three full-time occupants two toilets is superfluous. That space can be given to more important uses. I would recommend a tub/shower combo, thinking of resale when young families will want a tub to bathe little kids.

The entire wall with powder room, utility room, and laundry room should be condensed into one laundry closet with no toilet and maybe a utility sink.

Rather than the Murphy bed bedroom, I would consider having a second living area with a sleeper sofa, armchair, and a desk if you need one. That will be useful for your child to have guests over.

The woodstove is not a focal point. The furniture shouldn't revolve around it. Settle where you will put the tv and arrange the living room around that.

You're losing too much wall space for furniture placement with sliding doors. Each of those doors requires an open pathway.

Although lots of people love open concept homes, it's my opinion that long narrow homes quickly become bowling allies when they are open. So I would provide seperation between kitchen and living room.

One half of the front side of the house has no windows. The one window to the right of the front door looks into a bathroom. That facade won't be pretty to say the least.

Can the woodstove be moved? All in all I think the best arrangement puts a bedroom at each end of the house, with the guest bedroom/den/office near the child's room and the bathroom near the master bedroom. The front door would have a small entrance with a closet and lead directly into the living room with woodstove then into the kitchen. So looking at the plan from left to right I would have child's room, den, utility, kitchen with back door, living room with front door, bathroom, master bedroom. Or mirrored, depending on the lot and your preferences; I like eastern sun in my bedroom :) Hallway across the back of the house, balanced windows on the front.