The metro can be busy all day on certain lines regardless of so-called peak times. The terminals in some metro stations and metro bus stations accept bank cards (debit cards). Not sure if the accept credit cards yet. I would recommend using cash (pesos) for a metro ticket or loading a metro card. Not sure if they accept credit cards yet. Depending on when you come the metro will no longer sell individual tickets and the entire system including all the buses will be on the metro system card format by January 1, 2024.

Metro app by yalla-ya in the play store works fine and has been one of the main ones used in CDMX for several years. It's based out of Roma and the CDMX government uses its platform.. There's no official metro app operated by the government.

Pickpocketing is like in any other city in the world. Just secure your stuff. It's no big deal. Definitely not like Italy or Barcelona. I would say phone snatching is more at the top of the list in CDMX. They know they're getting something of value and don't have to dig in your pockets to find it. So, don't lay your phone on a restaurant table while being preoccupied and unaware of what's going on while sitting outside to eat regardless if you see others doing the same thing. When they catch this perpetrators they always have a boatload of stolen phones on them for just one day of snatch and grabbing, that ultimately end up in Tepito for resell.