Check out...
http://www.dendroboard.com/forum/care-sheets/
Tons of info on there.
Kinda full circle, because I found out about this forum from Dendroboard.
Tincs, leucomelas (the yellow and black ones in the OP's pictures), E. tricolor and auratus are all starter frogs imo.
Althought, auratus in my experience tend to be shy in the beginning.
There are also thumbnails, which are smaller, like Ranitomeya lamasi, vents.
I personally love the small guys...
Keeping dart frogs, imo, isn't hard...
If you do research as you would if you were to purchase a new fish, then you got the basics covered. The rest is just a learning curve as with all things.
It is keeping cultures of fruit flies week after week that is the most difficult for me.
Mine inevitably crash for some reason, and I have to overnight cultures to feed my frogs, which can get kinda pricey.
You could also check out the reptile shows in Hamburg, Havre de Grace in Maryland, and Whiteplains shows... there are usually a few dart frog vendors that can help you out in selecting a species to start with.
Hope this helps..