using multiple emails in the mail app and sending texts to that app as well
No. All SMS, MMS and iMessages are all collected in Messages.app. All email is, by default, put in Mail.app. There isn't any built-in way to merge the two. 

That being said, there is some flexibility to view multiple inboxes in Mail.app. While in Mail.app, go back to Mailboxes screen and select All Inboxes. You will see all the email messages from all of your accounts in a unified view.