Hello from East Yorkshire TRF , you are in a cracking area for trail biking ,the lads up that way should be along to show you the ropes but i must admit a bike will help you enjoy your day a little better !
try not to fall into the trap of thinking the bigger the better ,unless you fancy doing the odd enduro .....think more will i hurt myself pitching off at this speed as it will be part of a normal day out . So steady away at first . personally , only consider a bike with an electric start as it makes for a lot easier day especially when the going gets a little more challenging . See if you can contact your local group as thy can give you lots of advice and answer any questions you may have .
Enjoy ........Julian East Yorks TRF ...group rep .