1)
Why did David ask Nasan?
1.
Radak, Malbim: Nasan should ask Hashem [whether or not] to build it, and [if yes,] where to build it.
2)
What is "Beis Arazim"?
1.
Radak citing Targum Yonasan: It is a house covered with cedar wood.
3)
Was David concerned only for the Aron?
1.
Radak: He was concerned also for the other Aron, Mizbe'ach and Klei ha'Mishkan in Giv'on. All were under a curtain! He mentioned the Aron, for he spread the curtain for it, and it is most honored of all Klei ha'Mishkan.
