1)
Why did he say "b'Anyi Hachinosi"?
1.
Radak: David was not so wealthy, and he spent money in war.
2.
Radak citing Yerushalmi Pe'ah 4:2, #1: If he was Makdish after [the wealth] came to his hands, he is rich! Before it came to his hands, he cannot be Makdish it! Rather, it was within his four Amos. (He did not acquire it, but since he could acquire it, he can be Makdish it.)
3.
Radak citing Yerushalmi Pe'ah 4:2, #2: He fasted, and was Makdish [the cost of] his meal to Shamayim.
4.
Malbim: I was Makdish all my wealth to Hashem, therefore I was left poor!
