Hearthfire starts straight at the beginning but odds are you won't be building a house until you are levels 30-81
Not true. I have one character who started building a house around LVL 19-20, and it's almost finsihed and he's now at LVL 24. I have another at LVL 8, and she's got a good start on her house now. No need to wait until LVL 30-81.