WordPress custom login script

I am new to wordpress, but expert in core php. I need the following i) I want to build a software, where I need multiple level login(minimum 3 levels). You need to give some guideline, and available plugins for this ii) Write a sample plugin for creating widget (may be for travel packages), this should be written by you iii) Guidelines to develop a very basic template, but all important things should be noted. Regards,