Hi all, thanks so much for all the replies and recommendations.
The bike finally arrived home! and it did in great shape. I spend the last couple days working on it anyway, as the drivetrain had a lot of carbonized lubricant in it, specially the timing chain. The frame and paint are in awesome condition, I can't be happier with the purchase.
I had to order new brake pads, as the rear ones were worned out, but since the stoker and I really wanted to go for a ride, I decided to swap front brake the pads to the rear brakes, and remove the rotor in the front to avoid braking while there were no pads in there. We took a short 10k ride, and everything worked perfectly; those Avid brakes are outstanding, I can't imagine the braking power when both brakes are in working condition.
This weekend we'll go for a longer ride, on a hilly route, to check how that 3x9 drivetrain feels on our legs. So far, in the flat, we could both notice that there were a couple big jumps between some of the gears (because we are both used to 11spd cassettes), but that feeling might well dissapear when a bit more of climbing appears in front of us...we'll see.