EM5 how do you mix sound with video?

Hi I do a lot of stills stuff but am a complete novice when it comes to video stuff. What I want to do is mike up a dynamic mike to record a guitar amp also a condenser for vox and use the EM5 for the video at my home. What I have is a 4 into 2 mixer Behringer mixer or 8 into 4 16 track Yamaha digital recorder a usb audio interface Roland UA-25 EX which should take care of the audio side the computer is a windows 7 desktop and for video the EM5.

The end result I want is a decent quality vid for u tube to demonstrate a guitar and how to stuff for changing over pickups and phase splitting coil splitting and other techie stuff to do with amplifiers and Guitars.

Any ideas or links appreciated.

Cheers

Bob