What is "vi'Mrom Tziyon"?
Radak citing Targum Yonasan: The mountain of the Beis ha'Mikdash, which was built in Tziyon.
What is the meaning of "v'Naharu"?
Rashi: They will gather like a Nahar (river).
Radak: It is rushing. The same applies to "v'Naharu Elav Kol ha'Goyim" (Yeshayah 2:2).
What is "Tuv Hashem"?
Malbim: It is spiritual benefit. They will also come to due to physical success - "Al Dagan
Why will their Nefesh be "k'Gan Ravah"?
Malbim: Their spirituality will be satiated from His goodness.
What is the meaning of "l'Da'avah"?
Radak: It is to be sad and worried. It is Makor (like an infinitive). There is a Patach under the first letter of the root, like "Le'ahavah Es Hashem Elokecha" (Devarim 19:9)
Malbim: Due to the physical success, they will not be sad due to poverty and lack, like it says "Eini Da'avah Mini Oni" (Tehilim 88:10).