I know I can, but need help!

i'm creating a website for my college intercollegiate techfest. the fest holds a few programming events with other competitive events and a few workshops and seminars.
the website includes the basic info pages and allows the participants to register for different events.

now what i want to do is:

1) when a participant is registered(a user, role:participant), he gets a registration code. and once registered, he can register himself for different events(or competitions) which i'm putting up using webform.
2) now when that participant comes to college, he gives his registration code at the counter. the person at the counter(different role named registrar) enters his registration code(or the participants username) in and is displayed with the result of the webform the respective participant submitted plus some additional fields(preferably checkboxes) like cash paid, etc which he(registrar) can just check and submit.
3) also onsite registration where unregistered participant comes to the registration desk. now at the counter, he is given the registration code and is registered for events.
4) now the event(competition) organizers (role:event_oc) who organize the events, would get a list of all the participants in their particular event.
he can then check the participants which proceed to the next rounds or the winners.

i'm done with the first part, which was quite simple though!
but i'm having real time trouble getting through!!!

i'd request you all to please provide me with what i need or at least modules required to achieve the above functionalities.
i know all of these can be achieved, i'm trying and i'll find them some how! but if someone knows how to achieve these, please post in.
at the best, a list of modules associated with the above sections.