Houses are offered to you by the Jarls of Whiterun, Riften, Markarth, Solitude and Windhelm. In all cases, there are things you must do before you are allowed to buy the house, so you should speak to the Jarl and see what he or she needs you to do, as well as talking to their stewards for the same. Eventually the offer of thaneship will come up, this will typically open the opportunity to actually buy the house.
The museum is in Dawnstar, Skyrim.
You need to complete the 'Walking Nightmares' and then the 'Kill Giants' quest for Dawnstar. Then you will need to help three Dawnstar residents to become Thane. It is the only house in the Hearthfire DLC where you are required to become a Thane before you can purchase it.
He lives in Dawnstar.
On the coast, northeast of Dawnstar.
You have to go through the Dark Brotherhood questline. Innocence, my brother.
Go to the steward of the hold in which you want to build the house. You can only buy land in Falkreath, Dawnstar, and Morthal. Ask them to buy a house and they should offer you a plot of land. Also before you start the game open the Data Files in the Launcher, and make sure that Hearthfire is checked.
The Tower of Mzark is located in the Pale, south of Dawnstar. Source: Elder Scrolls Wiki page "Tower of Mzark"
no but there is a house in Winhelm that a side mision a girl was killed in
The nine holds of Skyrim are; Eastmarch (Windhelm) Falkreath Hold (Falkreath) Haafingar (Solitude) Hjaalmarch (Morthal) The Pale (Dawnstar) The Reach (Markarth) The Rift (Riften) Whiterun Hold (Whiterun) Winterhold (Winterhold)
Dawnstar was created in 1977.
to my knownledge there is no workbench in dawnstar
You should receive a courier message after you hit Lv20, inviting you to see the museum. But you can just head there anyway after you reach Lv20, you do not need to wait.