Average edges is a bit meaningless, because some do cost more than others. My characters tend to range between 5 and 20 edges, but typically delete with around 8-10. However, I do rack up a lot of exploration and observation exp, and typically get between 1k and 4k of imm exp. (One of my characters had much more than this, hence the 20 edges.)

Edges become available at different points, because they have different requirements, some of which may not be listed when you ask for prerequisites.

I tend to have an idea of which edges I REALLY want, and which are "nice to have". I also have a rough idea of what a given amount of various exp is likely to get me in terms of edges. This means that I will be able to form a reasonable judgement on whether taking a cheap "nice to have" edge now is likely to mean I don't have enough edge points for that REALLY nice edge later. Generally I can afford to pick the odd cheap edge or two without delaying how quickly I can get the first really nice edge.

Personally, I would take a couple of "basic" edges (e.g. calmed mind) and then save the rest for what I consider to be really useful edges (e.g. twitchy, or some of the class specific edges).