#1 and #2 are the important ones (though you could bump up #1 to 10 reviews or so to be even safer - though honestly, if she had 5 reviews from ALL very well-established reviewers - guys who have lots of reviews of VERY reputable ladies - then I think you are fine).
As I'm sure you implied, but others have also explicitly instructed you to do - read the reviews.
One VERY important thing to me is looking for guy's comparisons of her photos to how she looked in person.
A guy can say a woman is beautiful, but that is very subjective. However when he compares how she looked in person to her photos (same, older, heavier, etc.) that is much more objective and helpful.
Beyond that, use your own best judgement after reading the reviews, as a lot of this stuff is subjective and I'm sure you have an idea of the type of lady, service, and personality you are looking for (oh, and also, I suggest you DON'T let really really hot photos persuade you to give a girl a shot, even if her reviews aren't good - a strong consensus is usually right, and it's not like you will be the one great guy to magically bring out the best in her!).