I work for a nonprofit who utilizes volunteers for many different functions, from day to day operations to special events. In our current data system we are able to set up a portal so that we can post volunteer opportunities online, and potential volunteers can look through them and sign up for them. Volunteers can also keep track of their volunteer hours and we can have volunteer descriptions right online. I did not see a volunteer portal on your list of options, do you have anything similar available if we switch to Civi CRM?
Take a look at CiviVolunteer at https://civicrm.org/extensions/civivolunteer
CiviVolunteer is installed at the CiviCRM Demos. Enable it for an event, example click Volunteers tab on: http://d46.demo.civicrm.org/civicrm/event/manage/settings?reset=1&action=update&id=3