Hello Kate!
Whites are wonderful pets! I'm obsessed (I have 7, and got my first Whites over 20 years ago). I owned a lovely blue phase, Daphne, and sadly she passed away last month, but she was gorgeous (oh and very fat, I nicknamed her "Jaba the Hut").
I've never been familiar with a Whites being red. I've seen them dark, dark brown, or pale, pale green, or neon green, or shades of turquoise/blue. This makes me think the other frog was either very sick, or actually another species. It's always good to be sure to get healthy frogs (though I'm known to buy out my local pet store's supply pretty regularly as I feel they have sub-par care for their frogs).
I have had males, I have had females. I have bought captive bred babies, and I have bought full-grown adults. Personally I love them all! I hear rumor that males can become territorial, but I have never seen it. In fact, my boys tend to all curl up together every day inside the same hollowed-out log.
In my experience, I like keeping them in pairs. Some people say this isn't necessary, and perhaps it isn't, but I find they do tend to be social as they are often found sleeping near one another. I feel that it's because they like company (heck I would get lonely!). That being said, a lot of sources say pairs aren't necessary. They also don't breed easily (unless you set up a rain/monsoon tank) so you don't really have to worry about "accidental" babies. Furthermore, I find in pairs they tend to each pick a color and one will be green, the other brown. Just a weird thing I've noticed.
My recommendation is to get a captive-bred Whites Tree Frog because (1) it's not destructive to the environment like removing a frog from the wild; (2) it's less stressful for the frog as all they've ever known is captive life, so they adjust a lot better than a wild frog; and (3) wild frogs tend to be way more likely to have diseases and get sick.
It was really neat to get juveniles because I could watch them grow. My babies (Daphne and Dwight) went from being able to both fit in a tiny bowl, to a medium bowl that they then both couldn't fit in, to a large bowl. It's amazing as one alone could eventually not fit in the original bowl they both initially could fit in. That being said, they grow, and grow quickly. If you get juveniles, be sure your local pet store carries small enough food for them (some stores don't carry small enough crickets). Be prepared to up their food size eventually. Also, juveniles need to eat daily, adults do not, so juveniles are more care intensive initially. Juveniles you also can't tell the sex of, so you'll be playing a game of chance there. It isn't until they are adults with nuptial pads on the male you can tell. The other thing is, with juveniles it's tempting to start with a smaller cage because, well, they're small. Yet, they grow quickly and soon you'll be forking over more $$ to upgrade anyway, so I recommend starting with a tank big enough for a full-grown frog (or 2 full-grown frogs if you elect for a pair) so that you don't have to just upgrade the tank anyway.
I really don't think you can go wrong with juvenile vs. adult, or male vs. female. I will say this though, my males do love to call (the blow dryer, or a vacuum, or even the tv will set them off) and I absolutely love hearing their songs. If you would like this possibility, I recommend males, as the females really don't call (Dahlia will "call" for a couple second when someone is sitting on her head and she's mad).
No matter what, if you set up a good habitat, clean it regularly, provide fresh water daily, feed them well, keep a close eye on their health, keep temperature maintained as well as humidity, he or she should be a happy frog and can live a long, healthy life. Keep in mind too, these guys can live 10+ years, so they are a long-term commitment. The fact that you've already said you're "researching like crazy" is a great sign you are preparing yourself for the full care and best care of these little guys. I find them very rewarding and in fact, I plan to build a HUGE new terrarium for them (5+ feet fall, I hope!) for them soon. They're addicting little guys!
Lastly, don't overfeed them. They don't regulate themselves well in knowing when to stop and can become obese. For their own health, they shouldn't be overfed, and I also prefer to have mine have to be active to hunt because (1) it encourages natural behaviors; and (2) gets them exercising while hunting. However, many people hand feed their guys with tweezers or put them in a separate feeding cage. This has the advantage of being able to monitor closely how much they are consuming, and keeps the problem of dead crickets to a minimum. Also, I find if crickets aren't consumed quickly enough, they will get hungry and bite the frog, and I have had to give frogs oral and topical antibiotics to deal with the bite and subsequent infection. It's definitely a careful balance and you'll figure out what works best for you and your little friend.
