Hard Rock is a great all-purpose bike. For mixed riding, get the shop to swap out those knobbly tyres for a slick, or mixed use tyre, which you can run at higher pressure. You will go faster on the road, but still cope with well prepped trails.
Standover: straddle the top tube, put both feet on the ground. There should be a fair amount of daylight between the top tube and your 'nads. 3-6" is usual for an MTB, but some riders have more.
Once you have safe standover clearance, the most important dimension is length. The top tube length and stem combine to set the reach from saddle to bars. You want a position which is comfortable, not too upright, not too stretched out. You also want to be able to position the height of the bars. Most experienced riders would have them 1-3" below the saddle, some aggressive cross-country racers would have them lower