Hi Justin,
I would like to confirm the following information first:
1. What’s your location?
2. Have you purchased Office 365 already?
Normally, you can set up an Office 365 trial account from the website: http://office.microsoft.com/en-us/business/compare-office-365-for-business-plans-FX102918419.aspx. After trying Office 365, you can buy a subscription from Office 365 portal. However, in some countries, the users will have to contact partners to purchase Office 365. According to your description, I understand that you would like to use Office 365 Midsize Business. You can buy Office 365, and set up Office 365 services such as Exchange Online referring to the following articles:
Buy a subscription after trying Office 365
http://office.microsoft.com/en-in/help/buy-a-subscription-after-trying-office-365-HA103849166.aspx.
Set up your organization for Office 365 Midsize Business
http://office.microsoft.com/en-in/help/buy-a-subscription-after-trying-office-365-HA103849166.aspx
Install Office on your PC or Mac with Office 365
http://office.microsoft.com/en-in/office365-suite-help/install-office-on-your-pc-or-mac-with-office-365-HA102822111.aspx?CTT=5&origin=HA103849115
If you have any other questions about setting up Office 365, feel free to contact me.
Thanks,
Mindy Pan