Hi.. and welcome to the forums! If you have any questions, let us know, we'll e glad to help ya out or offer our opinion if you need be.
As far as how to become a reviewer, The only thing I can say, is it takes time. Most of the trusted reviewers have been doing reviews for quite a while, so they've developed a reputation that others can rely on. Most of the long term reviewers have been given consistent reviews over a few years, so we know their individual likes/dislikes, and can relate to one or two. They also have the charisma to do reviews.
Not knowing you, I have no idea, and most viewers wouldn't either. The best thing I could suggest, is to do a lot of out of pocket reviews. Do your honest opinion for juices, and be detailed. For hardware reviews, Experience is very important. It helps to know in depth how atomizers work, and potential shortcomings down the road with a new atomizer. I've gotten to the point where I don't really look at reviews that often until I'm ready to buy. I may then go for a few reviews to backup any concerns I'd have with the atomizer.
So, go start some reviews.. get working. As far as the giveaways.. I haven't really been looking, but I think ECF has a section just for that.