Hi Steve, I'm sure you will have a lot of fun with the Mavic when it arrives, it is one of the most advanced UAV's available.
No worries about flying in forests, in "follow me" mode, the forward and downward looking anti-collision sonar will guide it through the trees. Just remember to enable "find a way round" mode, otherwise it will stop and hover when it "sees" something in front of it. Although I have never tried the "Follow me mode", I suspect it may lose you amongst the trees. Also, when using "follow me", remember to set the "Dynamic return to home". Otherwise, when "battery low" automatic "return to home" is activated, it will return and land at its original take-off position.
I also fly a Phantom 2 vision + (my first UAV) and an Inspire 1 V1. As my primary form of transport is an Ebike, The folding Mavic is absolutely perfect, just a small carry case no bigger than an SLR camera case. The Phantom 2 is reasonably portable at around 4.5 kgs in its backpack. Just recently I have purchased a C11 backpack for the Inspire 1, 6 kgs with three batteries, haven't ridden with that much weight on my back yet but, it's just a matter of modifying the riding technique to suit.
Have fun
Fly safe