Thetford is the perfect introduction to MTBing. It was the first trail centre I've been to, after MTBing off and on for 15 years. I was amazed at how smooth the ground was. I'm used to rutted bridleways, horse hoof covered footpaths and rooty and rocky forest paths!
The switchback singletrack is great fun. The Beast is also good if not particularly beastly!
Once you've mastered Thetford,
Swinley has some more challenging routes.
That bike is a bit of a full on racing rig, btw. For recreational MTBing, most people are better off with a trail style bike with a slacker head angle (68 to 70 degrees, rather than 71 degrees as in that Cube) and a longer travel fork, 100mm at a minimum.