I've been very interested in the development of space for many decades now. Part of that reason is the basically unlimited possibilities that are available. Only limited by the short sightedness of those in power, and the unimaginative/uneducated/scared shitless masses.
But as to your problems of who and how have been covered very well above. Though I have something for you to consider. While manufacturing the components on earth and launching for assembly where manufacturing is readily available, the cost of 'shipping' will be the killer.
And to do the entire project in orbit sounds nice, as pointed out the requirement of building the facilities to do so would be time, personnel & material costly.
Of all the books and material I have read on the subject points out a option many miss. Build the main production facilities, and personnel housing on the moon! Gravity is 1/6th of earth. With no environment to worry about as well. And you have a source of raw material to mine and process to finish needs. Not to mention the fact that asteroid mining would be far more practical from that vantage. (Ages ago I dream that of being a independent asteroid shipper, find one with needed minerals, latch on, spend the next year pushing it to the refinery.)
As for the personnel? As pointed out by early responses, most of the engineering and management can, and should be, earth based. In part so as to minimize environmental needs. But who do you really need on both the moon and fabrication site? I agree with largely with what has been said in earlier posts. But as for skills sets? People with as many as possible to do what ever is in front of them. A plumber that can also cook, do basic computer programing or even pick up a welder. A electronic tech. that can do basic medical and more. So what will be needed is what I call J.O.A.T.s: Jack/Jill Of All Trades. Have one or more specialized skills, but a multitude of other skills.
And economics? Ask yourself this: with the near collapsing of the world economy, how many people would jump at that chance of chance of a better future, and the risks?