Why did Chiram send to Shlomo?
Radak: It was to establish with him the love he had with Shlomo's father David. If Shlomo wants anything from Chiram's land, he will give it to him, like he sent cedars to David.
Refer to 5:15:2:1.
Why does it say that Chiram sent his Avadim to Shlomo? In Shmuel II, 5:11, it says that he sent Mal'achim to David!
Malbim: The first time, he wanted to make a Bris. For this he needed Mal'achim, which implies an esteemed mission. There were nobles and advocates authorized from the king to make a Bris through the bonds they made between them. There was no need for a new Bris with Shlomo, for he is in place of his father. The Bris with David applies to his son who rules after him. He sent only his servants to bless him and ask about his Shalom.
