Awe we're always hear to help, especially those of us who keep White's. We can answer almost any question you have, just PM any one of us and we'll help you out. It's a pretty daunting task at first but once you start you'll realize it's a lot easier than you thought. Cleanliness is key, you never want to touch your frogs with dirty hands or chemicals like soap or lotion. As long as you keep that in mind, along with the specific husbandry rules for White's, you should be fine. I'm sure we all have faith!
You could probably keep a lot more than three to five white's in 149 gallon tank, but do what you're comfortable with, you definitely don't want to have too much on your plate. And as long as you follow quarantine procedures you could always get more White's later on and add them to the setup. I promise you if I had a bigger tank I would be going crazy with White's XD I might even try to add a partition so I could keep more than one species in the same tank. I'd be like a kid in a candy store! XD