For us, the major improvement in our quality of life was installing hot water recirc. It has cut down water waste and that interminable wait for hot water after turning on a faucet or the shower in the morning. If I were building a new house, I would also consider solar hot water.

For electrical, I dislike the looks of GFI outlets, so we installed GFI breakers instead. I would also consider adding more outlets than are required by code in places where you

As far as water treatment the first question to answer is well or municipal water system? If on a water system the water conditions will be more consistent and usually less expensive and complicated to treat than well water. If on a well there will be some education and maintenance required because you want to make the water nice and you have to make the water safe and monitor that it continues to be safe.

The next thing is a comprehensive water test by a certified lab.

If a softener is required then you need a location at the main water service with a drain, an electrical outlet, and we need to know the diameter of the plumbing (3/4", 1", 1.24") at the softener location.. Some people choose to plumb treated water to the house but untreated water to the kitchen and outside hose bibs. Some people choose to plumb treated water to everything including hose bibs cause they like how their car washes with soft water (just like at the car wash). Depending on water test an undersink RO can be installed in the kitchen for cooking, drinking, and ice maker water.

Then we need to know # of bathrooms, # of people, SFR of the plumbing,

I recommend the installation of 1/4 turn isolation valves where ever it is practical so that maintenance can be done on the plumbing in, say, the kitchen, laundry room or a bathroom or an outside faucet without turning off the water for the whole house.
Also, one frequent complaint is the sound of drain water, such as from a toilet, tub or laundry, which can echo loudly through other living spaces as it sloshes its way through the pipe. Drain pipe material, routing and mounting should take this into consideration.

It looks like a couple of the responses got cut off mid-sentence, so kind of hard to respond. What drain pipe material options are available that would make a difference? I thought it was just pvc or cast iron (or chromed brass at places like sinks where the plumbing is on display) with pvc having mostly replaced cast iron.

Are there any brands or materials I should look at specifically? Or things I should try to avoid? I've kind of read a mixed bag of things about PEX, although I like the manifold layout idea. Are there any gimmicky type things I should be on the look out to avoid?