The trains are 4-car insofar as that is the number of carriages you can walk between. They are actually operated in blocks of 1, 2 or 3 so in other words 4, 8 or 12 carriages in length. There isn’t currently any luggage storage but I’m sure they could be fairly easily reconfigured. What I will say as a regular user is the air conditioning is very good and they are about the most comfortable non-intercity trains I’ve travelled on in the UK.