I think Monreal should stay for now. Loan or sell Gibbs instead if we're bringing someone new in. Odds are he'd fetch a good price somewhere since he's homegrown and coming from Arsenal. Sunderland or Palace would probably be ready to splash on him. Maybe even Newcastle or Villa.
I think Ghoulam is a good player personally. Not sure he's ready to start for a club like Arsenal, but he'd be an upgrade on Monreal defensively and an upgrade on Gibbs going forward. Monreal's passing in midfield is pretty important to the attacking buildup though. Ghoulam or no Ghoulam I think he'll still start next season.