azure newbie

Where to start, I'd try and narrow down a few things

What licencing will they need for Office 365? For example,  Office 365 Enterprise E3 is a popular option but it depends on what they are after or is appropriate with costs etc. E3 includes almost everything a typical company will need, though there are some nice extras in E5.  

Exchange is also available standalone with Exchange Online Plan 1 or 2, as well as lots of other permutations like Office 365 Business Premium (max 300 users) or E1.  See the https://technet.microsoft.com/en-us/library/office-365-plan-options.aspx for more insights.

Another thing to consider is identity, in other words, how are they going to log in to Office 365.  Most companies want to login to Office 365 using their existing Active Directory usernames and passwords. This requires additional setup typically using Azure AD Connect which is installed on a local server and this syncs on-prem users into Office 365.  There is also an option for password synchronisation with Azure AD Connect as well as more advanced options like federation using something called AD-FS. There is a simplified option called Azure AD pass-through authentication, which is in preview, that will make this even easier. Azure AD doesn't cost anything when used with Office 365 unless you want extra features.  Here are some more details - https://docs.microsoft.com/en-us/azure/active-directory/understand-azure-identity-solutions and https://www.microsoft.com/en-cy/cloud-platform/azure-active-directory-featuress.

Moving on to Azure, I'd ask how are the going to https://azure.microsoft.com/en-us/pricing/purchase-options.  Using an Enterprise Agreement has advantages but there could be other options to consider.  For the SQL services, it depends on how this is to be deployed (IaaS vs PaaS), this has some more details -   https://docs.microsoft.com/en-us/azure/sql-database/sql-database-paas-vs-sql-server-iaas.

Backups vary, some at additional cost or can be provided via third-party services.   For Exchange, for example, you would look at https://technet.microsoft.com/en-GB/library/dn186233(v=exchg.150).aspx which is 30 days, after 30 days, the mailbox is permanently deleted and can't be recovered. Hold options are worth exploring as well - https://technet.microsoft.com/en-us/library/dn790612.aspx. Plus the https://support.office.com/en-gb/article/Set-up-an-archive-and-deletion-policy-for-mailboxes-in-your-Office-365-organization-ec3587e4-7b4a-40fb-8fb8-8aa05aeae2cefor Exchange can help with retaining items for longer after they have been deleted.  If this wasn't enough, a 3rd party option might be the next step.