Great questions!

> 1. What's the most populous arcology that's currently inhabited?

The term "arcology" hasn't really been embraced by the wider urban planning community, so in terms of self-identified arcologies, that'd just be Arcosanti, population 80-100. But arguably one could apply the term to something like Whittier Alaska (population: 318), Masdar City in the UAE (population: 1,300?), or even something like "The Line" in Saudi Arabia, which, when I talked to them a few weeks ago, already had 17,000 people on-site. Lots of projects in China probably qualify, depending on how far you want to stretch the definition. A few may even have been built -- there's a lot that's just on paper.

> 2. Do the seasteading people and the arcology people have much overlap?

Not that I'm aware of, although I'm sure there's at least a bit.

> 3. Are arcologies aimed at making affordable housing or no?

One of the great deficiencies of Soleri's forumlation of Arcology theory is that he incorporated virtually no concept of urban economics, so this question would've just been out of scope, from his perspective. Which is a problem, because it's a good and urgent question, and needs to be answered. Doing so would require evolving the notion of "arcology" well beyond how Soleri defined it, however. (And in my opinion that would be a good and necessary thing, since otherwise it's a largely un-realizable theory.)

So from a more personal perspective, I'd say that making housing more affordable is something which arcologies ought to be aiming at, and given their general frugality -- via minimal land use, maximal sharing of resources, etc. -- should be achievable. But there are many devils in the details which are yet to be worked out.

(Also, it's worth pointing out that "affordable housing" itself may actually be a too-narrow formulation of the problem. Net cost-of-living is probably a better way to think about it. Perhaps your actual living space is actually a bit more expensive -- but given that you don't have to spend any money on a car or gas or insurance or even public transport, then that really ought to compensate. Or perhaps your personal living space is a bit cheaper but a LOT smaller -- but given the fantastic public amenities at your doorstep, it's a richer life overall. In other words, what needs to be optimized is the whole-life package, not just the cost of a domicile. Although obviously the latter does need to be within reach, in a way which for many people it currently isn't.)

> 4. Is anyone working on incrementally built arcologies, or is that just a city?

I'd say that yes, people are "sort of" working on incrementally-built arcologies -- and that's not simply a city.

Again, this is an area where Soleri's formulation of Arcology theory is quite deficient. He always thought about arcologies as things that are wholly self-contained (although not necessarily self-sufficient; he thought that was a false ideal) and built from scratch. There are places in the world (mostly Africa and Asia) where building whole new cities from scratch is a very real prospect, but for the most part, the developed world isn't going to (and arguably shouldn't) do that. In that case, the question is whether the principles of Arcology are something that can be adopted incrementally, and if so, how to do that.

My personal answer would be that yes, there are ways these principles can be brought forward piecemeal in existing cities, via projects that (among other things) promote high-density, car-free, mixed-use development. Here's a good example of such a project, also in Arizona: https://culdesac.com/

There are limitations to this kind of approach, but it's definitely a good start.

> 5. There is basically no discussion of agriculture in the article; is anyone working how arcologies integrate/improve the food system?

Yes! Integrated food production has long been a concern at Arcosanti (and of Arcology theory in general), and there's been an on-and-off agriculture program there, as people willing to take it on have come and gone. This has recently been re-started and re-energized by an independent nonprofit called Arco Agritecture. You can read about them here: https://www.arcosanti.org/arco-agritecture/. There's also a newsletter signup etc. here: https://mailchi.mp/50d2bae3774b/v0z8xb894p

Hope that helps!