I have a pair of hybrid shoes (Brooks Cascadia) which are good on the road and adequate for light trail, although master of neither. Anything other than light trail, and you are into the specialist trail/fell shoe category (Salamon/Inov-8/Merell/Scarpa). I have a pair of Karrimor Trail Run (Sports Direct - £40) which I use for the wet stuff.
If you are going to be doing a lot of off road mountain running, then I would go for a dedicated fell shoe, and stick to road shoes for the hard surfaces. It's always good to rotate between a couple of pairs of shoes.
I have used a hydration system (Nathan XC-Race) on longer training runs (over a couple of hours), and during a trail Marathon, but never anything shorter. Most of the 10k's I've done have a water station at the 5k point. That should be more than enough; even in the height of summer.
If you do suffer with hydration issues, then a bottle belt or a small hand carry bottle should be enough to keep you going.