I think if I were designing it, I'd want to build it around a small river, with river beaches on either side.
Lots of swimming, kayaking, rafting, floating, etc. can be done on the river
Have a huge park(probably a circle with a 2 mile diameter) surrounded by apartments
Within the park have a few schools, a library, lots of sports fields(baseball fields, tennis courts, volleyball nets on river beaches, etc.), a few grocery stores, a cafe, a health clinic and vet clinic(and be within a 1 hr drive of a bigger city with a hospital), a small fire department (which would also have ambulances that could rush you to the hospital in the bigger city), a small sheriffs office with 2-3 deputies (assuming we are our own county), outside the apartments we could have a golf course, bike trails (downhill etc.), Costco, county/town building, etc. things that we need/want occasionally, but not often enough to be in the park.
Ambulances, firetrucks, sherriffs vehicles, etc. are the only vehicles allowed in the park without a permit, all construction equipment etc. needs a permit, cars stay on other side of apartments. I'm guessing most people wouldn't own cars, some would own cars and use Turo or something similar to rent cars to whoever needs them when they aren't in use.
Apartments would be 200-1000 square feet each, the park could only support a small town, I'm not sure the exact amount but probably somewhere between 3,000-8,000 people, so we probably only need the apartments to be 3 story max apartments. If the town ended up being a big success, someone could use the knowledge learned from it to modify the design and make another one slightly up river
I'd put in a Gen4 nuclear reactor just outside the town (they are testing many variations, we'd go for whichever makes the most sense), maybe this could be a main employer of the town, providing generation to ourselves and selling to surrounding areas as well.
Heres a very rough draft