incredibleworkethic -
I would suggest you spend some time on the demo that they have setup, you can run thru the front end to see it's functions, and then spend time with the admin area and go thru all the admin functions, it's pretty easy I think, but you might have a different idea of what easy is than I do
Sorry to say, but every time I've ever made big changes to my sites I always seen a drop in traffic, but I've also been very fortunate and it always has come back up in a few weeks
Just be very diligent about getting the 301's in place, and make sure that your sitemap is the way you want it, and you should see a pretty quick recovery. I normally have a shell into my server and I watch the error logs for any 404's so I can fix them on the fly. All the big SE will re-hit a page that it finds an error on in a day or two, so if you fix the 404's as you go, there shouldn't be any issues!
Plan for double the time you think it's going to take, first time out of the box I spent a couple of weeks going thru all the options and getting my feet wet with MB, the last one I setup took like an hour to get it all setup plus the template changes I wanted to make.
Good luck
