Make sure you get a liquid test kit like this one: http://www.fosterandsmithaquatics.com/product/prod_display.cfm?c=3578+4345+4454&pcatid=4454
although the price of it is higher than the dip strip tests, you get far more tests out of this kit. Also, dip strips are very inaccurate and notoriously produce false positive readings when combined with some dechlorinators. You might want to take a small container of your tank water when you go to the fish store because the fish store will test your water on site for you for free.
If the ammonia in your water tests high at the store, your fish might benefit from a methylene blue treatment. It works well on parasites and ammonia poisoning.
Also, if you get an adjustable heater, you should get one that is 25 watts.