I'm no expert but do a lot of offroad/trail running including the london-brighton trail run a few years back. obviously shoes are a very personal choice depending on foot shape, drop preference etc. but in my experience you really can't get better than inov8, with my own personal favourite being the roclite 295. great for mud but enough cushioning for hard packed ground as well. shop around online and depending on shoe size you might find a bargain !!
stumbled across this thread by accident but really interested in the warm up advice by Dachs. Don't consider myself a beginner but usually run long distances although this year and next 'coming down' to 10k and maybe a few park runs.
Some years ago I got a PB at 10k after poor planning meant I had to cycle 6 miles at top speed to make the start time, I always thought the PB was despite the rather frantic, high intensity warm up, maybe it was because of it !! normally I just jog about a bit and throw in a few strides and stretches.