Website Tree Structure [closed]

Question

I am currently helping redesign a poorly built website that suffered with a case of PHP spaghetti.

In an attempt to structure the site I have the following tree (apologies for the length):

http://www.domain.co.uk     -   Root Directory
-   /

-   /our-service
-   /our-service/pricing
-   /our-service/mobile

-   /search
-   /search/results
-   /search/results/<page_num>

-   /resources/announcements
-   /resources/competitions
-   /resources/email-archive/<email_num>
-   /resources/sitemap

-   /contact
-   /contact/advertise
-   /contact/support

-   /legal/terms
-   /legal/privacy

-   /<username>
-   /<username>/reviews
-   /<username>/reviews/<review_id>

http://my.domain.co.uk      -   User Account Area
-   /instructor

-   /instructor/account
-   /instructor/account/activate/<hash>
-   /instructor/account/password
-   /instructor/account/email
-   /instructor/account/contact
-   /instructor/account/status
-   /instructor/account/close

-   /instructor/billing

-   /instructor/reviews
-   /instructor/reviews/disputes
-   /instructor/reviews/ratings

-   /student/account
-   /student/account/activate/<hash>
-   /student/account/password
-   /student/account/email
-   /student/account/contact
-   /student/account/status

-   /student/review
-   /student/review/past

-   /student/theory
-   /student/theory/new
-   /student/theory/results

-   /logout

1) My first real question is if anyone is able to spot anything that may cause an issue further down the line using this structure? Obviously /<usernames> will be checked against a reserved list to prevent any issues in that sense.

2) In terms of error handling I have seen several methods used on websites, one being url based. For example, an error with a username/password could be displayed using /login?error=mismatch. Is this a better approach than doing things invisibly behind the scenes or is there no real advantage?

3) Finally, the site has two parts to its registration (student / instructor) with the student having a single page to complete, and the instructor a multi-page form. I can't figure what the best method would be to implement it into this structure.