Hey Kai, give what input I have for you.
I've seen people that have retaining wall/foundation next to house use a coating to pervent what is called "efferesence".
I don't know what it's called off hand, maybe a paint/concrete supply.
From memory, I think there is plenty of light/sun, I wouldn't think you need the expense of solartubes.
Your siding was old aluminum, fairly resistant, I think you were planning stuco anyway?
But they also make a vulcanized(rubbery) paint that would protect, and you may consider pond area for that even after stuco, as stuco alone is permiable.
As for humidity, you may notice it a little bit, but wouldn't stop me(and I know won't stop you)
I'm not a pond expert, but will help w/ fasteners and such where I can.
I also have a pretty good book on Japanese style ponds you could borrow.
There's a fine line between owning your tank, and having your tank own you!_________________________________________
120G SCA starfire, tunze 1073.02 return pump, Geisemann reflexx 4xT5, 2x panorama pro LED strips, 2x Vortech MP 20's, 40g sump w/ fuge.