How to fit a replacement tailgate on estate mk2

So, my car got too friendly with a tree amd to cut a long story short I need to replace the tailgate and offside light housing. I've managed to source these in the correct colour but need advise about fitting please. What problems may I encounter? What kind of cost? I've a very capable friend who thinks they can replace in about an hour but just want to see if there any hidden issues we may not be aware of. Thanks