Exporting video for first time - didn't set sequence settings in beginning?

Hi,

I created a video made up of clips of many different videos I downloaded online with fair use or no copyright.  I downloaded most of them using 1080, but some only had 720 available.  Others from pexels were probably higher.  I didn't know to set my sequence before I started, so now that I'm exporting I don't know anything about this and how to set the setting for the best quality.    I watched a video but it seemed they knew the camera settings before they started and started with a sequence setting to match.

I've worked for months on this so I want to be sure to export to high quality.  I will not be putting it online, I am going to upload it to dropbox or save on a thumbdrive. If anyone has any tips I'd appreciate it.

Thank you!