You need to be level 9 to do anything Hearthfire related. Also, you can't have a bounty in the hold you want to build a house in. At least, thats what I found. My level 7 dude didn't recieve any letter after days of consecutive waiting. But after turning level 9 and fast travelling to the Whiterun stables, BOOM, there he was.
I did it all at level one. Anyway, only bug I had is that two of my three houses didn't auto-decorate when I paid the steward. I don't intend on using
any of the houses, so it doesn't bother me, but it's kind of odd that I have staff living in a completely empty house. I don't feel like manually adding stuff for them. When they said you could buy materials from your steward, I assumed they meant ingots and everything else. It's too much work to decorate a home you don't want to live in when you have to hunt down resources.