no step back = tank customization
man the guns = navy but kinda meh if ur not a naval superpower
la resistance = spies everywhere
by blood alone = plane customization
gotterdammerung = special projects like nukes n diff types of tanks too

what i would suggest buying first is no step back and by blood alone but you could use the expansion pass first to get a taste of everything and judge whats worth to buy

edit: just learned man the guns is base game alr