WP-based project –how?

Ok, I’ve had a brainwave this morning in the “novel uses for WP” department. I won’t go into the detail of the project. Suffice it to say that I’ve been looking into ways to create a web-based, collaboratively maintained database of a certain type of spelling error/slip/lapsus (if you are really interested, google for “eggcorn”).
While my coding skills are improving, I’m not ready yet to do this from scratch. That’s where WP comes in. An entry would consist of: the “word” in the title, the “correct form” in a custom field, and then fields for a) usage examples and b) interpretations would be needed. The body of the post could replace b), ie contain an analysis what the particular error means. Categories would be used for languages, subcategories for particular subtypes of lapsi.
If I’m optimistic, I’d have about a dozen registered users (everyone could register and then post), three or four of whom particularly involved. Static pages (WP 1.3) would be used for general information, posting rules etc.
Problems:

• Every user needs to be able to edit everyone else’s posts (solved — know how to do this).
• Permalink structure: /%category%/%postname%/ — is this feasible? Better would be /%category%/%postname%/%number%/ where number disambiguates posts with identical names (there should be very few of them).
• Can I define custom fields that are lists of strings? I’d like to have one field for each usage example, but it’s impossible to know how many usage example would be added in a single entry.

Any help is appreciated!