It depends on how your LEA are going to be migrating to Office 365 as to what infrastructure they are going to put in place, and to be honest depends on how things are setup at the moment as to what approach I would take if I was to do this kind of migration. They will use 2 ways to do the migration it will either be a Staged Migration (CSV Batch Migrations) or/ a Hybrid Long Term Co-Existence Migration. But they will handle to creation of new users and the mailbox data migration for you I would assume.
In regards to User Creation afterwards, If they are using Single Sign On with ADFS then you would probably use the current process and so when they create a new user within AD they will also create a Remote Mailbox and this will be in Exchange Online. If they do not use Single Sign On then you may be given access to the Office 365 Administrator Portal and so you can create the users yourself... if they are going to use a Global Tenancy for ALL SCHOOLS then they are going to have to look at the permissions around this. I doubt they will do individual tenancy's per school although I would of recommended this way if possible.
This would all involve discussion, it depends on what they are planning and I can't really answer that for you.
In regards to how Office 365 works, you will basically login to https://portal.microsoftonline.com which will then give you access to Exchange/Lync/SharePoint etc. if you just want to access OWA then you can browse to http://outlook.com/schooldomain.sch.uk and this will take you straight to Outlook Web Access. On the credential front again it depends on how the LEA are going forward, if they are using SSO then the credentials they are using now will work... but if they are not going down the SSO Route then they will provide you with a new password as it will be using Local WAAD (Windows Azure Active Directory) with No Sync between On Premise Active Directory via ADFS.
I hope that helps,
If you have any further questions feel free to poke me.
For the user creation, they may populate the accounts for you, in which case you would then need to double checked the assigned license for the features you want them to have (exchange, sharepoint etc) and then maybe reset their password once the migration is completed. Otherwise you might need to create the users from CSV, then provide the login details to the LA to migrate from Easymail to O365. Best bet is to check how they want it done.
For e-mail they can just go to mail.office365.com and login with their account details for OWA access (and they also get the links to skydrive, sharepoint etc along the top if they are assigned access to them)
If they use outlook, then you just need to add a new Exchange account wizard, enter their e-mail address and it should go off and auto configure the rest of the settings. If you are running Office 2010, you need to make sure you install msoidcli_32bit.msi (available from MS downloads) so that it does not keep nagging you about user credentials.
If you are using Office 2013 then it works straight out the box.
The LA have asked for usernames and passwords just for the easymail accounts - I think they are just migrating the email to Office 365 - presumably they would expect us to log on to the Outlook Web Access.
That is ALL they are doing - certainly no SSO or AD stuff
But what happens if I set up Office 365 at school myself - how would I integrate it with the email that they have set up? My users will want it all available when they log on to office 365, they won't want to log in AGAIN to get their email?
If the LA have only done the email bit then how can the users get access to sharepoint etc? Surely that goes with the Office 365 set up that I will be doing?
thanks @EduTech and @Boredguy
NB - we currently use easymail with the web interface - no outlook
You need to find out whether each school will have its own tenancy. If so, you'll essentially have your own management portal. If they're going down the shared route, its up to them what permissions they delegate. I could see it becoming a real hassle that way so I'd ask them if they can migrate mail to the tenancy you've made/will make.
To add, if you setup Sharepoint on yours and mail on theirs, there would be multiple logins. This also gets complicated too in terms of cookies O365 may get confused over the logins.