First of all a big thank you to everyone who posts in this forum as I have found the answers to many questions I have had in the past.
But I am now in need of a bit of help and I have not been able to find the answers I am looking for so I would be grateful for any help or advice anyone can give...
I have been asked by my brother-in-law to record his wedding for him.

I have two relatively budget mv camcorders (one a panasonic GS80 and one the Canon MD235). My plan is to set up one camcorder at a fixed location on a tripod to record the whole of the ceremony (ie bride and groom) and to use the other to wander around and catch the atmosphere. I then hope to be able to edit the two together so that it is not one long shot of the ceremony.
BUT, and it is a big but, I have never done anything more than point and shoot before. So I have never edited anything. In fact I have never even plugged my firewire cable into my computer so even moving the footage off the tape and onto my computer will be new to me. I am relatively techie so think I can manage the basics but even so...
So, a few questions if I may:
Am I being overly ambitious?

Should I use the built in mic of the canon or use an external mic plugged into the canon? If so any suggestions for (a cheap?) external mic?
Or, should I ignore the sound on both camcorders and see if I can beg, borrow or steal a separate (presumably digital) recording device from somewhere?
Assuming I then have three tracks (two image tracks and one audio), can I edit them together relatively easily? Or to be more precise can I edit the two image tracks together and then get the audio track to play over the top whilst managing to synchronise the mouths with the sounds? (I guess I should play the audio and main track simultaneously on the editing programme and then just slot sections of the second track in? Is that how it works?
Assuming the above works (and putting to one side copyright issues) can I then lay pre-recorded audio over the track eg to have a music track as an intro blended in with background noise while people are arriving?
Does anyone have any other tips or suggestions that I should be thinking about (except perhaps to forget it and get a professional in as that is a non-starter I am afraid!)?
If this plan is a possibility then I think I am going to need to get some editing software and then a digital mic but other than that is there anything else I will need?
I know I can get suggestions of editing software elsewhere but based on what I plan to do, has anyone got a suggestion of a very simple editing suite that will let me do all of the above whilst (a) not totally confusing me; and (b) not costing me the earth!
Thanks in advance for any comments/suggestions!