I'm very sorry for your loss
I wouldn't use bottled water. Tap water is fine, just treat it with a dechlorinator. Prime is my favorite but other brands like AquaSafe will work. Remember to treat all water going in the tank with it, including top-offs.
You were right to question the pet store's suggestion of gravel (sounds like they wanted to sell you gravel). Bare bottom is the easiest to clean (although you can cycle your 5-gallon and in that case may want substrate) but sand (regular play sand is fine, just wash it really well) and larger rocks work (they sell "smooth river rocks" that are a good size).
A 5-gallon is large enough to cycle and keep stable so I would suggest you do that if possible. You have a few options:
-Purchase Tetra SafeStart and use it to seed your tank with "good" bacteria, allowing you to add new frogs immediately
-Add a pinch of fish food to get the cycle going and keep testing your tank and adding food until it's stable (0 ammonia, 0 nitrite, some amount of nitrate). Do a partial water change and add the frogs.
-Get filter media from someone who has an established aquarium and either place it under your substrate or in your filter (even just a piece cut off). This will achieve the same effect as the SafeStart.
The second option will take the longest but won't require having to track down a mature aquarium or spend money on SafeStart.
Read this thread on aquarium cycling: http://www.paw-talk.net/forums/f77/c...ium-43789.html
Let me know if you have any questions after reading that. I know the chemistry can be overwhelming to new aquarium owners but it's not as bad as it sounds!
For live plants, there are some hardy low-light species that are nearly impossible to kill. Try java ferns, anubias, water wisteria, java moss, and/or flame moss. Java ferns will even happily grow under basic incandescent lighting (do you know what type of lighting you have?). Live plants will speed up the cycling process and make things more stable. They could also potentially save you if you accidentally add frogs before the tank has finished cycling--many live plants will absorb the toxic ammonia.
Make sure you have the following before trying new frogs:
-Heater (get one you can set to a specific temperature as opposed to one that just heats randomly)
-Thermometer (glass or digital, avoid the sticker ones that go on the outside of the glass)
-Basic freshwater aquarium test kit (you at least want tests for ammonia, nitrite, and nitrate)