What did Hashem mean when He instructed Yakov to leave, and promised that He would be with him?
Rashi: As long as he remained attached to Lavan (whom Hashem described as Tamei), Hashem's Shechinah would not rest on him, and only after he returned to his father's land would it rest on him. 1
Seforno: He promised that He would guard him on the homeward journey. 2
Ha'Emek Davar: After he returns, Hashem will be with him to guard him from Esav. Hashem had not promised to guard him from Lavan.
Did Hashem tell him to return right after Lavan and his sons started resenting Yakov, or some time after?
Malbim: Initially, Hashem wanted that Yakov stay there, so all were pleased with him. Now Hashem wanted him to return, so Yakov heard and saw the ill will of Lavan and his sons. 1
What is "ul'Moladtecha" to which Hashem told him to return?
Ha'Emek Davar: It is to his way of serving Hashem through Torah and Avodah. He should return to his father's land, but not to his father's house (Esav was still angry).