I don’t understand why everyone here is so obsessed with obsolete loco hauled trains. My preference would be a level boarding battery bi-mode 730. (Obviously not a 730 but something with similar layout and interior). Maybe a bit more luggage storage. The 1/4 3/4 door arrangement would massively speed up dwell times.
If we have magic money tree, I would go for all 10 car trains, with 10 rows in the middle section, and 5 rows in each end section. Without infinite money, I would do a uniform 8 car layout, with 6+11+6 (3 more rows per carriage), minus luggage racks. Likely around ~600 seats per train (slightly more with 10 car), triple a current 4 car.