I have both Rivas and eGos. Other than slight cosmetic differences and the button, they are pretty much the same. I do prefer the button on the Riva, but I prefer the silver band on the eGo. I've actually moved to mega eGos as my preferred batteries most of the time, but only because they last even longer. There is no difference in function.
I know a lot of people like the low resistance atomizers, but I prefer the regular 510 atomizers that come with most of the kits. You'll do fine starting with that.
The juice and mg level is very subjective. I would strongly recommend getting samples of a few different things so you can start to figure out what you'll like and what you won't. Get some different pg/vg mixes, different flavors, different mg levels. I was surprised to learn that I don't like any of the tobacco flavored juices I've tried. (I've tried a LOT of juice.) If you'd like to know where to get samples, let me know.