Autism

Use Mold Earth (Cantrip) to ensure the land on the island is mostly/all clay and to build an artificial aquifer with channels for water to flow down into it
Use rafts and piles to build solid foundations for housing
Use wooden frames around dry stone walling, molded into air tight walling (using the stone to make holding pins) using the Stone Shape spell
Use wood chips and sawdust, as well as other useless materials, for cavity wall insulation
Use the wood flooring for the cave so we can have a start-up base
Use various spells (Stone Shape, Mold Earth, ect) to expand the cave
Use standard wooden docks for water access
Expand the source of the in-cave stream to a lake for airship refilling (as well as electrolysis-based gas creation if we can get away with it, but we don't expect to)
Build fortifications using various spells (Stone Shape, Mold Earth, ect) and standard building techniques
Get a town with a trade going
Stockpile resources in granaries
Grow town
Build further as needed
Expand on to further islands as needed
Generally grow the town to a city
Make mad tax dollar
Live like kings
We'd also need a teleport hub so we could get from place to place quickly
This would basically give us fast travel, as well as a hub from which to work from
Had a discussion with a mate of mine about the architecture of our town. We can get away with high gothic if we're a very religious town. This means if we can get Althur on our side, we can do high gothic, meaning spires, towers, vaulted rooves, stained glass. big wooden doors, that kind of thing.
Plus, considering I get specialist training for working on oil rigs, we can sink rafts and piles, get ourselves a base further out to sea
Get ourselves a Mother Base going
A blend of the two, smaller houses saxon style with anything bigger in high gothic, might work
Plus, with stone shape, we can work out designs to etch into the walls of the big stuff
And as a man with an art professor for a mother, I know pigments for glass. Also, split styles would be better if it was quartered. Residential, market, religious/military and gorvernmental.
Saxon in residential, southern market town in the market, high gothic in the gorernmental, mixed based on religion in the religious but high gothic for anything state sponsored, such as the church of Torm and the military.
I've had an idea to get us a permanent fresh water source. We open the mountain up to have a caldera, build a massive tower in the middle for us to actually live in, run a copper rod down it to attract rain and storms, set up airship staging platforms around the edge with covered stone bridges leading into the tower. When we get access to Wall Of Stone, we can straight up make bridges and walls and shit, make an entire building, minus detailing, in 10 minute
If we really want to improve the foundations with magic? Compact it down. Mold Earth can turn regular clay into superdense near-ceramics with pressure, leave micropores for the water to trickle down into the aquifer. We run a Wall Of Stone through it, that'll have carbon and silicon enough for us to be building on some true bullshit hard foundations
We're looking at a 9 to a 9.5 on the Mohs scale
I fucking LOVE silicon carbide
Times like this, I remember why I enjoyed materials engineering
We can also build a Mother Base out of the stuff
And make coins out of it
We can run our own currency, with a standard gold conversion rate set by trade
People bring in bread, which sells at a copper a loaf. We charge one... let's call them Denarii for now for a loaf of bread. Exchange rate set
We expand our trade empire, slowly acquire a monopoly, then offer slightly better rates in our currency.
BOOM
We control the entire system of monetary value
Besides, if we're doing that, we're going full ToH. Get stone doors enchanted to be as hard as adamantine. And we are going adventuring. I just want somewhere to call my own when I lay my head to rest.
If that so happens to be the single biggest trade city on the island, so be it.
That's all the info we've got sorted so far
I've also worked out a system of government for us to work off:
Meritocratic Socialist Ogliarchy with a bend towards Capitalist Libertarianism. Means everyone has the same opportunities, rights, and responisbilities on a macro level, but free trade is a hard fact and freedom is a given for all citizens.