1. Think vernacular - it is what's called passive house certification now, just a fancy way of using the materials and the design methods that are most suitable for your area of the US. Here in Florida, it is for instance, the overhang around the houses that helps with the cooling in the heat of summer.
2. Insulation - preferably the double walls with the deep window sills - saves money forever.
3. Practicality
This is your chance to address your families needs:
No weird steps and stoops - if you want to live there in old age - also a hazard for little ones.
Doorways wide enough for a wheelchair - usually 48 inches and a clear path through the house - especially in and out of the bathroom.
Standard size windows do save a bundle or do like our friends did - buy rejected, odd size windows once they had a general plan and integrate the ones that worked for them. Many of the window shops will be happy to work with you on this.
Research the heating options to the nth degree. I vote for floor heating and a fireplace, plus a stove that can use different materials for heating.
A thousand times yes on the accessibility of pipes and electrical. Quite expensive to rip into walls or hunt down the problems when you can't get to anything - not to mention the inconvenience - if you are handy, it could save you thousands.
All rooms must have a window and I insist on a nice size window over the sink in the kitchen.
Agree on the solar tube skylight, if possible.
Decide on bike storage, a separate, spacious laundry area as well as sports/camping whatever equipment or holiday decor storage areas - and easy access to them - from the beginning. If you make it an afterthought you'll live to regret it.
Think about all the homes/apartments you've lived in or visited and what you liked best about them when you do your own planning. Even if you go two stories, with all bedrooms upstairs, plan for a room on the main floor downstairs, near a bathroom, that could become, if ever needed or wanted, a separate space for a long time visitor, teen, invalid or older adult that can no longer manage the stairs.
I'd still look at plenty of homes for sale new and old, just to see their flow and get a feel for how it would be to live in such a layout. The devil is truly in the details - well thought out solutions pay off forever, think long and hard about what is important to you and make sure you incorporate at least the top five things on your wishlist.
In this case, mustachianism to me means get the best you can afford, if it brings long-term satisfaction, is important to you or saves forever on your utility bill.
Kitchen and bathrooms top my list of pet peeves for poor design - I hate bathrooms where if you spread out your arms, you touch the wall - even in the shower. It is supposed to be a room, not a dingy closet!:) with no windows and poor airflow. Then people wonder why they have mold - duh!
Heck, even the Romans of two thousand years ago had floor heating and spacious bath areas and thick walls - just sayin'.
Good luck!
PS - yes, I use a clothesline, because we live in Florida and it is better for the life of your clothing, perhaps for the environment too, but I did plan a space with electrical wiring already in place in the utility room for a dryer when the time comes that I am too feeble to hang my own laundry.
Since I had to grapple with an impossible floor plan, 5 foot by eleven foot, I elevated the water heater when it needed replacement anyway. It sits on a heavy duty shelf up anchored to the concrete block walls, so I have plenty of space for a dryer beneath.
I ran high and deep shelving on the other wall for holiday storage and placed the rolling tool chest beneath - it isn't easy to fit today's lifestyle in a 50's small bungalow.