1)
Here it says that he took from Tivchas and Kon. In Shmuel II, 8:8, it says from Betach and Berosi!
1.
Radak (6): Each city had two names. Betach and Tivchas are the same, just the letters are reversed.
2.
Malbim: Their names changed. There it explains that Shlomo used the copper to make the Yam (a Mikveh), pillars and copper Kelim.
2)
Why does it teach about all the gold and copper that David took?
1.
'Rashi': Refer to 18:1:1:1. Rashi (Shmuel II, 8:7) says similarly.
