The definition of Speed, Energy, and Leadership, and how they apply to your Age 2 Evony Hero, is a needed information base, when it comes to attacking your enemies and NPCs.
The Speed attribute speeds up your travel time, it does so by dividing the normal travel time by 1+0.1*MountLevel. For example, if it normally takes 140 seconds to get somewhere and you have mount level 4 then it will be divided by 1.4 giving 100 seconds.
Hero Energy seems to be a certain number out of 100. Every time your hero marches he looses 4 of his energy points. These energy points will recover over time. This means that your hero, cannot constantly attack one or more enemies, as he needs to rest after a while. Thus it is more important then ever, to have multiple heroes.
I read on the forums that each level of Leadership, allows you to command 1000 troops effectively. If you send more out than this the hero can support then there are increased losses. I don’t think it increases losses directly, I think it reduces the effectiveness of the extra troops so they might only be fighting at half their capacity. For example, if you send 100k archers with a 60 leadership hero, I suspect 60k will be at full attack and the remaining 40k will attack at a reduced level which would be half. You definitely seem to get a lot more losses attacking NPCs with low leadership level. I go around 40k losses with one around 60 that in Age 1 I’d have expected only around 20k losses with. If I’m attacking with 90+ leadership now, I get losses similar to what I would expect in Age 1