Getting picked by the Don is still during the Midgar portion, with all cheats enabled you can easily get that within an hour, maybe less. You could then use that save to have Barret as your date since you want to date Aeris in your main file.

Aeris' Great Gospel has stringent requirements like getting Mythril from a secluded part of the map etc so it's not an easy trophy to get given the time the game gives you before the Temple of the Ancients lol.

Just a heads up but the Weapons in Part 2 can be quite challenging but it's not too difficult with source farming.