I've seen people power grab even if they were raised in the best of environments.
Power Grab will always be an issue, no matter the environment.
Hm... I think I realize what you are getting at... however, let's try to examine that:
Being raised in an environment that DOESN'T prompt you to pursue power grabbing is only 1 step.
Those who did grow up like that but eventually decided to 'grab power' probably did so because they were eventually encouraged to change enough so that they would 'seize power' due to the system they lived in (the present socio-economic system).
See... having 'noble' people is not enough.
You need to design a system that actively removes the possibility of ANYONE 'grabbing power' and discourages such behavior (via education - no force or 'indoctrination' necessary).
If you don't, well, like I said, Human behavior can change, and in the present setting it changes to accommodate the existing socio-economic system if an opportunity presents itself (because that's the kind of thinking society at large promotes).
This is why a TRANSITIONAL period is required. A temporary setting that would allow Humanity to adjust which would do away with the old system automatically at the end of the 10 years time-frame (providing there's a global push to initiate this change - however, Humanity is already in a transition period of sorts).
Lack of relevant general education is a big factor here as well that cannot be disregarded.
Most 'noble' people who change for the worse later on were never exposed to that and in combination with the present socio-economic system, its a rather 'easy' recipe for disaster because they allowed themselves to be used by others and the system they live in.
The notion that there would be 'too many cooks' as it seems is a bit of an assumption.
Seeing how most of the construction will be delegated to machines and most everything would be automated... ideas proposed by Humans would be taken and compared with existing models. The less viable ones are discarded or simply put on the side to see if they can be combined with the more viable ones to create a better solution.
A computerized system would have to do it seeing how the process would be WAY too complex for Humans (computers have already surpassed Humans a long time ago in the department of specialized tasks) - in the end, whether we allow final construction to be made is up to us - which is why any given community or self-sustaining city would arrive at such decisions. Putting the entire globe into whether or not to construct it in a local area is not necessary (apart from how to possibly improve upon the ideas).
As for technology 'eventually breaking down' - as I said, self-maintaining machines and machines that make other machines already exist - all of which would render this issue mostly moot.
We can make technology materials that are practically next to indestructible, that will last for 'absurd amounts of time' and can be made in abundance.
We can DESIGN technology to eliminate most, if not all stress related factors that contribute to degradation in the first place, and automated processes would simply recycle older machines by harvesting their materials and created superior machines (software/hardware that improves on itself).
Perhaps there's a possibility that it won't last until the end of time itself (if such a thing even exists), but it can certainly be designed to last absurdly long.
Add enough safe-guards to take care of most of these issues and most of the 'problems' are rendered moot.
We ARE talking about 'sustainability' after all.
In the end... I do agree with most of your ideas KamenRiderBlade and way of thinking.