What are the best practices for ETL of data from one OLTP system to another?
Use the tools that you are most comfortable with. Your situation seems simple and lasts only for a short time. If you have to keep this up and running for a long time, you might end up by using more advanced tooling, where you define rules for conversions and synchronizations to be performed for you. Doing so is easier to maintain and to document. The learning curve might be a little steep.
On the other hand, you could use this case to train yourself. There is no urgent deadline and when it gets more urgent, you probably build the home cooked version within a day.