How has he overcome the devastating effect of micrometeorites? A force field?

I imagine our laser tech these days is up to it. Scattered micro lasers to target and destroy any micrometeors.

Isn't this overly reliant on a fictional design at the expense of practicality? While you might be able to get the three engines to keep the ship straight, a breakdown would cause a continuous spiral. Put the big engine along the central axis and any auxiliary engines symmetrically around the side. Then put your gravity wheels anywhere along the main axil. The original Enterprise design was for a ship which did not need to obey currently known physical laws because of a "warp bubble" Without that, the reason for the Enterprise become nonsense.

It's ambitious. I like it.
Here's the thing. If we can send enough robotic manufacturing out to the asteroids, we don't need any people out there for a while. Let them build a large factory first. Very soon not only would it be self sustaining, it would allow us to the flexibility to colonize the moon and mars.
Plus if aliens do show up, having the Enterprise in orbit would be a great deterrent. "Hey, we thought it was just a TV show!"

While I love the Enterprise... it is probably one of the least efficient designs ever contemplated for a space vehicle.
I do agree that we need to do SOMETHING. I just think that the Asteroid Mining guys have a much better plan to make our move into space a reality.

Albert Einstein stated that if your motion was to reach the speed of light. Your mass will be equal to energy. Not that you will be energy. Your mass with your forward motion combined would be greater than energy alone and you would thus be expelling more energy into the universe than absorbing and be a universal source of energy.
The trick was to created a static warp bubble or static warp field that would drain and absorb energy from the contents in the subspace of the bubble. The warp bubble is traveling at the rate of speed of energy and you being some of the contents in the warp bubble would not be in motion as you would be out of this bubble.
Hyperspace is the result of how the warp bubble interacts with the outside universe. The warp bubble putting it's contents in the realm of space that there is no reaction of energy and giving way to faster than light travel.
Your also missing the plasma injectors between the engines magnetic thrusters and is needed to move through Hyperspace.
There is no deflector to create a warp bubble.
The ion engine is the impulse drive.

What we need before any planning is a list of all known aspects this is likely to face, then design solutions for each point with redundancies and then and only then do we design it. I applaud his efforts on this but a global forum needs to get together first and figure out as many possibilities and probable threats from spiralling off into the void right down to being scoured by space dust. Yes this should definitely be on kickstarter. Before the only way to unify your people was by identifying the enemy (us vs them), now we are socialists lol (facebook etc.) we have turned the bend we can do this together (them IS us)

If we are going to build a spaceship based on a fictional design Arthur C. Clarke's Discovery could be built with our current understanding of physics.

First things first. Before going to the moon, or anywhere else, we need to build a space elevator. This would allow quick, cheap transport of cargo to a city. The city (new earth) would take advantage of zero gravity to manufacture goods and launch spacecraft. It should be self sustaining in every way and sovereign. First things first.

If I had the money I would have McKinley Station built. My McKinley station would be a full-fledged space resort with suites, restaurants, a zero-g spa and recreational facilities, docking bays [for shuttles,] and ship[-building] yards.