A 5.5 year old that behaves well should e fine on that trip. But TPAC flights are often 13 hours long!
Expect to bring your own toys and kid snacks.
The 2 of you will be quite isolated.
Have you looked at the F menues? Have tou looked at the cabin pictures of the isolated seats? It is impossible to chat between seats in that cabin; even between the 2 inside aisle seats. Also, the NH F cabins are quieter than a library. Neighbors do not want to hear conversations.
youtube has many NH F trip reports for your review.