Trial Versions and the Mac App Store

I just bought a MacBook Pro last week and downloaded from developer websites trial versions of several applications I was interested in buying based on my experience with the iPhone and iPad (OmniFocus, Bento 4, Pocket Money), as well as Mac Versions of PC software (Office:mac). I have decided already that I will be buying some of the titles and I was wondering do I now buy them from the App Store or do I need to go through the developer sites again. I know that with Office:mac it's not in the Mac App Store so I will need to buy the app from a retailer or through the Microsoft site, but at this point will probably not get Office.

Will I have to delete the apps I am interested in and then get them on the App Store or can I leave them on the Mac and buy them from the app store. The App store does not recognize any of the apps on my Mac, even the iWorks and iLife apps that came with my Mac on the day I bought it.