Well, the drip method is pretty much a good idea under any circumstances as it's essentially the least stressful way to acclimate a fish to a new tank.
You did mention that you wanted to add the other species (likely even more sensitive to water parameters than the Discus
) first. I do kind of doubt that the LFS is keeping their fish in different parameters (other than "easy fixes" such as using crushed coral as substrate in the African cichlid tanks). That said, if their Discus
are being kept at parameters similar to your tap, their other fish (tetras, rams, etc.) likely are, too. So in that case, I still think you'd be best starting with the harder, more alkaline water and slowly converting to the "ideal" environment once the tank is stocked.
Again, this is all pending the LFS's water parameter numbers and could end up being a moot point.