Flavours are something you can only really get your head around by trying them. A lot of vape shops (the ones in my city anyway) have a ton of sample CE4s set up with different juices to try before you buy. Just remember they use food flavouring mostly, so banana juice won't taste like munching on a ripe banana, it'll taste like a mcdonalds banana milkshake, which actually tastes nothing like banana.
Most, if not all, juices get better with time(take a search for steeping) so don't give up on one right away, let it sit and come back to it in a few weeks.
CE4s are pretty durable little fellas in my experience, never had one blow on me or give a burnt taste (unless I accidentally let it run out of juice). Just keep it topped up. I never had a problem with switching juices but I usually stick to fruit flavours so they all taste relatively similar.
In regards to the warning labels, I maintain my view that they are there purely to make my life difficult because my flatmate, to this day, thinks I carry bottles of military grade poison around with me and wont let me take them into the kitchen (she's fine with plumes of vapour floating around though). It's similar in use and imortance as the "may contain nuts" warnings on bags of peanuts. That said, don't drink the stuff, it tastes horrible and makes your lips feel funny, and don't drip it in your eyeballs, it may give you a quick nicotine hit, but it would sting and you'd look like a pillock.
Also, look into evods. Fantastic piece of kit, similar in size to a CE4, just fills up from the bottom and provides much better flavour and much more vapour and the heads can just be switched at a fracion of the price of a new CE4. They can also be recoiled for pennies if you want to delve into the world of rebuildables and re-wicking and re-coiling, but that side of vaping is filled with tinkering crazy inventors, although we all seem to get dragged in.