Lots of good suggestions have already been posted. Here are a couple I don't think anyone has mentioned... Lights in our walk-in closets will be wired to door switches so that the light comes on automatically when you open the door and goes out automatically when you close the door - like a refrigerator light. I'm hoping this set-up will also help me train DH to CLOSE his closet door instead of leaving it standing open all the time! Several outlets in the soffits way around the house for plugging in Christmas lights - all are wired to a single switch for ease in turning lights on/off. Extra lights in our stick-built attic space with a switch by the access door so we don't have to use flashlights to find stuff stored up there. Everyplace I've ever lived had one light in the attic at most. Even with it on, the thing you're looking for is always in some other corner that is dark. Mirror defoggers in the bathrooms (a very inexpensive luxury!) Outdoor lights specially positioned for reading when one is sitting on our porch swing. A floodlight positioned to shine up and into the stained glass window that is in our the stairwell so we can enjoy it at night. Lots of extra electrical outlets around the exterior of the house.

How airtight is your new house? The Spark and equivalents are direct vent and get outside air from the outer pipe in the chimney. The glass front seal the combustion chamber, so no combusiton gasses escape. The examples on modernrustic all appear to not be direct vent and I would worry about getting enough combustion air for a big burner in tight new construction. I think I would call moderrustic and ask them and check with a local fireplace builder to see what they think.

Building custom vs. a tract home is always more expensive as mentioned by others. Buying existing can be more or less expensive depending on the area as it is very dependent on the market value of a home in the area. It essentially comes down to what are buyers willing to pay in the area, includes some adjustments based on location, features of the house etc. and the market value sets the house price of existing homes. This has very little to do with how much it cost to build the house to start with.

Pitiful but may be ok. You are looking at it all wrong. It is not the lumber it is about if it is plumb and leveled esp at the windows. It is not about foundation bolt - it is about if any of them are missing more than 6' apart and and 2x at the corners. It is not about the OSB flooring, rather if OSB was glued and fastened properly.... Sheathing same way can not end in the air.