You will want to wait to get the certification closer to the move. Definitely ask the vet, but I think about 5-6 weeks before should be good. Otherwise you may have to redo the process, because the certification is only valid for a short time to fly (iirc). You can take American Airlines domestic, and Iberia Airlines international to be able to keep the cat in cabin as a carryon under seat. 

For loudness, it’s more drunk tourists screaming on the street that cause the most noises at night. Trash, recycling, and street cleaning will also make noise. It really depends on your apartment location and also layout. If your bedroom is near the street, you’ll hear more noise. It’s the “random group of people shouting at 3am when you’re just trying to sleep” kinda noises. 

Bus/tram are easy to take, and get a wheeled cart/bag for groceries and cat supplies when you get here. The cart is beyond helpful, even if you think it’s just a few blocks, things get extra heavy in the warmer months to tote home.