Two Outlook Profiles Simultaneously

No, it is not possible to open 2 Outlook profiles simultaneously.

You can change the option in Control Panel -> Mail to prompt you for which profile you want to open every time you start Outlook.

Having 2 profiles is not a requirement for having two Microsoft Exchange accounts in Outlook 2010 or newer. However, you should make sure your primary Exchange account is added to your Outlook profile first. There are certain limitations (albeit minimal) when the second Exchange account is added to an existing profile. One of them being you can't remove the first account once the second account is added, and the rest elude me at the moment.

I run at least 2 exchange accounts on a single profile in Outlook 2016 (and have since 2013) and don't notice any drawback whatsoever.