One thing I have learnt from hedgelaying, is that "you are always laying for the next man". (or woman) It makes you think about the future and what the hedge will be like in 20 or 30 years time. And the same thing applies to fencing too. Don't mix the hedge with the fence - it just means that you can't maintain the fence and yes the hedge will push your fence around (posts and wire). It's also very hard to remove stock netting from inside a hedge.
Hedge on the foot path side - if you use protectors on the edge plants I would have thought they will survive just fine, unless your footpath is like the M25?
Clipex & horses - like any fence you want to keep your horses off it, even if it's wood, they will damage
most all fences ... hence I would suggest you use a strand of electric wire along the top of the inside - clipex make standoffs for this purpose (google "clipex insulator"). I would do this even if you use timber posts as horses will lean into your wire to get to the nice bits of your hedge.
As others have said speak to your local contractors/hedgers for more advice - they will be able to come and look and get a better idea of the best course of action
.