No, they don't all look like supermodels. Very few would come close to being confused as a model.
In general, yes, most "high class" (aka, high charging) escorts are pale skinned (not necessarily caucasian, however), slim (sizes 8-12, however there are quite a few size 14 girls too and some very thin ones; I think it's proportionality) and above average attractiveness. Most do not have educations any higher than other escorts: they fabricate and lie as a marketing pitch. I have never noticed a trend with hair colour, eye colour etc. However, crazy hair dos, bright red hair etc generally would be a no.
You don't need to be under 30 (it works very well to be older, not every man wants to be seen in public with someone so young it brings into question if they are paid or a golddigger), you can be of any ethnicity (however, people are inherently racist. They tend to see a western or northern euro as "worth" more than an eastern euro, many clients openly discriminate against Romanian's etc. Some clients think that black women will be more aggressive or risky, that latina's will be full on and "crazy" etc), you don't need to initially have a flash website.
If you are a attractive (even moderately so) woman that is not substantially overweight, in decent shape and can hold a conversation - you are in a good position to charge the same rates. Clients do expect a little more polish, good communication, entertaining conversations and do expect a good service for that price.
There are outliers to every situation.
There are many ways to make money. Some women like to work at lower rates with higher volume as it's more consistent, some want to work as little as possible due to commitments they have, or because they like to think of themselves as certain things.
The best thing to do (IMO) is to start low and raise your rates over a long period of time where your reputation reflects it.