Don't mess with pH. All the fish should be fine as long as your pH is stable (unless they are wild-caught).
With the dwarf gouramies, make sure you know how to identify females as most LFSs only stock males and go for a trio (1 male, 2 females) rather than a pair. Actualy, I would suggest going for a hardier species (ie honey gouramies - colisa chuna/sota) instead as dwarfs are notriously prone to internal bacterial infections which you wouldn't want to risk itnroducing to a tank containing rams (which can easily catch such things).
I'd also add some more cories or rasboras and consider that, if your rams were to breed, any bottom-dwellers (ie your cories) would get bullied. The more cories you have, the less likely they are to be harmed by the rams. The minnimum group number for the rasboras is 6, for the cories its 4. Both, realy need more added to their group.
Having said that, 3 dwarf gouramies, 2 rams, 6 harlequins and 4 or so cories would only just about fit into a 22 gallon tank. At least, if you switch the dwarf gouramies to honeys, you'll be saving a little space as honeys stay smaller. Also, I'd add everything except the rams. Wait a few months, then put the cichlids in. Not only will this allow your tank time to mature and stabilize, it'll mean you'll know whether you can keep up with the number of water changes necessary for your stocking levels and you'll be more familiar with your tank's limmits.
Alternativelty, skip either the rams or gouramies (I'd skip the rams because of the cory clash issue - but I preffer gouramies anyway

).