This is an interesting question.
- All the goods required in large bulk volumes are Refinery exports
- not all of which can be produced by mining and converting at a Refinery Contact
- so to get basic self-sufficiency, the hardest step is going to be setting up a Refinery which can supply in 28 days the necessary commodities to build a new outpost
- your limiting factors are probably going to be Liquid Oxygen and Insulating Membrane. (you need more CMM, but it regenerates so much faster, and you need more Steel, Aluminium and Titanium but can top them up through local mining and converting the ores)
- so you need an economy which can produce about 2000t of LO in four weeks
- which probably means a baseline supply (if you're not going to be messing around maintaining favourable BGS states) of about 250t
- which should be doable with a fairly small economy size of about 5000, which could be spread across multiple stations.
- getting an economy that large through colonisation hasn't been done yet, I think, but shouldn't be that difficult once we've figured out a little more
- now, what about Insulating Membrane. You only need about 10t a day... but that probably needs an economy size in the tens of millions. That's not going to be practical, so we use a different approach for that.
So you'd want a minimum of two systems, probably, both somewhat built up. (You might be able to do it with a single very large system, but it'll probably be easier if you can isolate the two different System Economy Influence buildings you need)
- first system is your Refinery. You go all out in this for Refinery Hubs and Colony stations they can convert into Refinery economies, plus whatever slider-affecting buildings boost productivity, until you get to the production threshold you need on Liquid Oxygen. If you've got space, throw in an Asteroid Station to more efficiently feed your Refinery Contact for Steel/Titanium/Aluminium. Make sure at least some of your Colony stations are surface, for the CMM production, and at least one orbital for Insulating Membrane.
- second system covers the rest. You build an Industrial and High-Tech Outpost (which have terrible production rates at baseline, but still more than good enough to build an outpost a month) and then build a Colony station to be converted to Agricultural by nearby settlements (if you get lucky, the settlements will also produce something you need). This system doesn't need to be as large. You may need to throw in a Large Industrial Settlement somewhere here to get yourself a local Refinery contact.
- Your Insulating Membrane you'll need to get from mission commodity rewards in the Refinery system, because you're not getting it from the markets any time soon! (this is what the orbital refinery station is mainly for)
- If you've got a Fleet Carrier to use as storage, you can afford slower production in the Refinery system, because you can stockpile an Outpost's worth of supplies on the carrier for two months - or even two years if you have to - then build the outpost with those.
That's got you covered for everything you need for orbital construction and getting your initial claims through in time. So you can from there continually expand your region and build up a few more production centres at this point. It'll be very slow to start with, but you can get at least theoretical self-sufficiency relatively quickly.
But ... surface constructions need Emergency Power Cells too. And they're only produced by a tiny number of bubble systems, and you can't add more in deep space... I don't think there's any asset you can build which lets you steal/salvage them ... and they're not available as mission commodity rewards. So you can't be completely self-sufficient yet for all construction types.
(A FC full of EPCs will last you a while, but you're going to have to send it back for more eventually)
(Getting the settlement to the point where it's more efficient - rather than just theoretically possible - to produce locally rather than to have a rolling set of FCs freighting cargo out of the bubble ... well, that's going to be a much longer task. I'm not sure it's even possible to build colonisation economies that large yet - we'll see...)