Hmm.
How about we change things to be similar to BM? Like say casters need to meditate every 12 hours? Make energy recover in this way while make concentration gained over time. Instead of us gaining 1 xp per hour, maybe make people spend concentration to gain xp?
so to summarize,
energy - required for casting spells. magical energy which casters need to gain
concentration - needed for casting spells, earning xp (reading books, studying runes etc)
