If you want to get one of these, I'd suggest you stick with a single male and keep him alone in a 15-20 gallon tank (though the larger the better). They are one of the hardiest fish around and will tolerate not only your high pH but low temperatures as well (they don't, therefore, need a heater - though one is strongly reccomended).
Single males can sometimes be kept alongside shrimp if the tank is quite heavily planted and there are large pebbles or ceramic pots or other difficult-to-access hiding places for them to hide away from the paradisefish.
The big downside to these fish is their aggression. They are extremely territorial (the males, particularly) and will attack both each other and other tankmates. Unlike many other gouramies, paradisefish are also perfectly capeable of catching the sort of small, active fish - like danios or barbs - normally kept with more aggressive species.
If you plan on a group, you need to go for a single male with
at least 3 females, plant very heavily and allow about 10 gallons pe fish. Large rainbowfish and most catfish and larger barbs will work as tankmates in this sort of setup.
Keep in mind that, if they decide to spawn - which they do quite readily - the male will become very aggressive and will pose a serious threat to his tankmates.
Other than this disadvantage, paradisefish are wonderful fish and full of character. If you are prepaired to give one a tank of his own, you should definitely go for it
