I can second Penguinmoon's opinion on the lounges. The AF lounge is extremely limited in terms of food options available and it feels like it's tucked in some random basement of BOS Terminal E. The BA lounge is much better but you will require OW status to enter the lounge since they only let me in on the basis of my QR Gold status and not the Business Class ticket.

You can change your seats and get the new boarding passes for your QR flight at the gate.