I’ve build all three, and here are some finding I’ve found that may be helpful. (xbox360)

Adoption:
You’ll need to build the “bedroom” wing, then the two kid beds and chests. Or obviously just furnish the entire wing. Move the wife in (I did this with at least the entire house and wings build and some furnishings.). Next Riften, and the orphan house, there are other orphans in towns (kids running) around to may be able to adopt as well (max two). If you’re having problems, you may have not met all the requirements but the woman in the orphan house should prompt you.

Land/House:
You have to be thane of the three towns that are offering land first, if not first do the quests to become thane and you’ll get a housecard and the option to buy the land will be available.

Building:
My third house was the most successful. First before anything, make a new save – this way if you don’t like the layouts you can undo with a re-load. Any new saves should be new one, obviously so you can still go back.

Build the house, hall-house and then your wings you want. DO NOT MOVE THE ENTRY WAY IN THE HOUSE (basically gives you different furnishing options but overall bugs.) When you‘re building, don’t furnish anything until it’s all built. Once all done, make another new save; this way, again if you don’t like or have issues you can re-load. I would built the internal anvil in the den first or soon, this way you build nails, etc. without going outside to the other anvil.

You can build everything yourself or get a steward – these can be any of your housecarls from other houses if want, the female elf student from the magic collage is available and others. Have them follow you to the house and they may comment on it and offer their services, if not – talking to them may show the dialog to hire them. Now – they can furnish your house (given the coin) but I’m not sure it’s all the items of the workbenches, I tried and waited 3-4 games days (with empty house) and nothing ever came, so I did everything by hand but then also paid – I found eventually small items will appear but it may take a long time – the hardest are the wall mounted items so if you pay, eventually they will appear. The floor mounted trophies however will have to be built by hand.

Workbench glitches: sometimes going to a bench will show all items, even though you’ve already build stuff; just back off and re-click – the second time usually displays correctly. Note that the first floor hall house workbench controls items there and upstairs – the upper bedroom only controls items above the den (bedroom area, top level.)

Extras:
Careful not to buy all three chickens, if fact maybe wait till you have everything else – otherwise the options may disappear and you won't be able to get anything else. First I bought a bard, then the horse carriage and then the other extras. Note: they may not appear immediately, so just go quest and come back later.

Missing housecard, wife, kids and steward – during the day this may happen, I don’t call it bug they may be walking around outside or just away, they come back so don’t fret.

The Bard may sing on top of chair, but then doesn’t get off – I usually approach here and she’ll get off – I’m not sure if it’s purposely or path issue.
Sometime you may come home and all the doors are closed, strange but nothing to worry about.

Since I (when I find or can) have taken out as many Talos patrols or teams -- I was near my main house and a hit team tried to take me out – pretty cool actually, I found “orders” on a dead one too – that’s an extra lol, not sure if its hearthfire or just a long range game trigger.

Anyway, happy house building.

Just a small note- you don't need the bedroom wing to adopt, nor do you need to be married. You only need to add the two small beds and a dresser to the top floor of the main hall and that will be enough to match the adoption requirements.

..i saw no point in this :L

you also don't need to be a thane of any hold to buy land. Other than whiterun, I have no titles, yet was able to purchase 3 plots of land. As long as you do the holds main quest, followed by a minor quest, then you're free to purchase what you want.