When did he offer Korbanos?
Radak: In Divrei ha'Yamim II, 8:12-15 it says "Az He'elah" - after the Bayis was finished and prepared for Avodah. (a) The copper Mizbe'ach was in front of the Ulam for Temidim, Musaf for Shabbos, Rosh Chodesh and three festivals each year. (b) The Kohanim were arranged in divisions. (c) The Leviyim were arranged in divisions of singers and gate-keepers. All was like David commanded him.
Malbim (24): It was after Bas Pharaoh ascended; in Divrei ha'Yamim II, 8:12 it says "Az He'elah" (then he offered). As long as she was there 1 , it is as if the Bayis was not completed.
Malbim: The Olos of the three festivals he offered from the king's money. Also Ketores on the gold Mizbe'ach was from his money 2 .
What is the meaning of "v'Hakter Ito"?
Rashi: This refers to the Mizbe'ach in front of Hashem, for Ketores. Radak - it was Ito (with) the copper Mizbe'ach in the Mikdash, even though it was in the Heichal and the copper Mizbe'ach was in the Azarah, in front of the Ulam.
Radak, from Targum Yonasan: It is as if it says v'Hakter Alav.
Why does it say "v'Shilem Es ha'Bayis"?
Radak: Everything was prepared for Avodah, like I explained (refer to 9:2:1:1). In Divrei ha'Yamim II, 8:12-16 it gives the details [of the preparations], and concludes similarly "Shalem Beis Hashem."