I had all that, just no easily accessable Corundium(had to abandon it due to some combatants dancing around each other for hours of real time somewhere). And this latest game there is 100k total in Sol, 70k of which is on a comet . still I like how I've handled this start best of all.
Note that for even 10 million population in orbital habitats you're looking at something like 75-80,000 build points AND resources. That will take a decently productive low-tech homeworld a decade or more, even if you have the minerals. You will also need tugs and freighters.
everything with habs can be build via Factories like PDCs. Thats how i do my 100 mining-module Miners. Just dont add weapons or something like that, the maintenance on for Habs is enormous. If you want to defend this brick just add a ton of armour and 2 or 3 seperate defense satelites - or a small corvete.
Hmm, habitats are too big for my immediate concerns, I have many smaller yards and slipways building vessels rather than a few large ones that I'd need, research and time will have to do.
Orbital habs are quite usefull for places where domes are no option, say if you have a world with low gravity (less then 0.15 G) or a say system with just some Asteroids. They are also quite usefull for Miners, Gene-modification centers and Terraformers.
If you've got the duranium and lift capacity its more than viable to establish domed mining planets. 100 regular mines requires 5 million workers, figure about 15 million population, 200 infrastructure per population or 3000 infrastructure. That's only 6000 duranium. The biggest problem is the freighters.
Orbital Habitats only become viable when you're looking at planets like Titan, and even then they are only sorta better than mines+infrastructure... and definitely worse than auto-mines. They have a hidden advantage in that they don't require agriculture/environmental expenditures above normal though.
You can use tons of infrastructure as well, orbital habitats are for when even that isn't an option. the problem with habs is getting them from A to B, but that aside they are actually quite worthwhile.
The first mineral I always have a shortage problem with is this one, and the only way to get more of it is with it it seems. My latest game for example has no easily habitable worlds in 40 explored systems, and while I have a flood of terraformers being built, towed around, and so on, in the intermediate it won't be enough. Are orbital habitats worthwhile in this situation? I'd have to put terraformer construction on hold to do so. Should I have moderated mine construction on the homeworld, and built some more automines instead? I've got 500 regular mines, and no where to put them now in the short term, though habitats could solve that.