1)
Why did he say "Gadol Kevodo bi'Yshu'asecha"?
1.
Radak: When You will save him from his enemies, his honor will increase in the eyes of the nations.
2.
Malbim: After Sha'ul died, David's honor increased via Your salvation. All Yisrael anointed him and he succeeded in his wars.
2)
What is the meaning of "Teshaveh"?
1.
Rashi citing Menachem: Teshaveh, Tasim and Tashis are the same matter (putting).
2.
Malbim: [The glory that You gave to him] was Shaveh (proper) for him, according to his deeds.
3)
What will give to him Hod and Hadar?
1.
Radak: Your salvation. All nations will honor him when they see that his salvation came from You.