First off, get as much detail on a character as you can, and not just physical details. Mannerisms, how they talk to complete strangers to people they're close with, who their relatives are if any and their relationship with such. Basically, Try to build a complete portrait of the character beyond what they look like. same with a location, don't just go with what it looks like. What does it smell like? Is it hot or cold? are there any odd noises? as the writing saying goes, "show me, don't tell me".

As for pricing, alot of people charge by length. Could do a set price for a certain length, then charge extra for every paragraph beyond that.

As for character registration, no clue.