1)
What is the grammatical form of "Shov"?
1.
Radak: It is Makor (like an infinitive), but the first letter of the root is omitted. It should be Yashuv. Even though normally we do not find Makor like this in which the first letter of the root is silent, there are exceptions, e.g. "Yadati Ki Chol Tuchal" (Iyov 42:2) is like Yachol.
2)
How will Hashem build them?
1.
Malbim: With kingship and conduct.
3)
How will Hashem plant them?
1.
Malbim: The nation will increase.
4)
What is the consequence that Hashem regrets the evil?
1.
Malbim: He wants that there will be a remnant and hope in the land.