Hi Tarnish! Good luck on your new Zith family. To answer some of your questions, here's my take on things:
People cash out lodging for various reasons, most of the time it's so that they could stay in line with in-game history (wanderer, traveler, etc). Other times they want to purchase items on their own, cashing out lodging and then buying stuff as they need it, a tent here, a horse there... Your plight's nearer the second reason, especially since you'll be having a family.
If you buy an acre of land as the Price List (see Masterlist link at the header) says, remember that it will be undeveloped land. You'll have an acre of land with nothing on it. If you're going to "start out" with this land, you can just deduct the cost from your CS as an initial purchase, and you'll be good to go.
Purchasing a "cottage" or "cave" as a settlement in the wilds may require storyteller permission. Different domains need to adjust to the needs of its own citizens. I hope that you have also checked the Zith wiki, as it provides a clear xplanation of Zith colony dynamics. For specific Zith questions, I suggest you direct them at Gillar. For asking about having your own settlement in Kalea, I suggest contacting the Storytellers of Kalea, specifically the DS of the city you want to be near in.
Adding "rooms" in your "house" require extra costs (again, this is explained in the Price list wiki.) Nobody has really done this, partly because of the cost involved. I'd like to foretell that one of your future inquiries may involve "pooling family resources". Kindly see Gossamer's scrapbook post titled Stooging
http://www.mizahar.com/forums/post43141.html. It gives insight of might be required and expected from you in the future, especially since it seems that you might be having slaves.
I hope I helped in some way.