What it boils down to is playing D&D, but using the 5th Edition of the Hero System to do it. OK, maybe not exactly D&D, but sort of D&D. D&D-ish. No character classes or any of that sort of bollocks, but lots of monsters and magic, and PCs doing really, really strange things in an everyday fashion. Plus dungeons, of course — got to have lots of dungeons.
As time passes, you may gain a Reputation perk (and/or disad) which may help to mitigate this disadvantage. Then again, it may just make matters worse.
I've created a new Characteristic, MANA, to deal with the problems involved in END use for magic.
It's base value is 10 and costs a ½ point per point to increase up to the Normal Char. Max. of 30, and 1pt per pt thereafter. The NCM goes up as you get older — to 45 in middle age, and 60 in old age.
You draw END for spells always in this order:
Mana is normally restored fully by a night's rest, though the rate of restoration may be adjusted upwards or downwards by the ambient Mana level of the area you're lurking about in. Some areas are more magically potent than others, while some places are barely magical at all.
A character with a negative Mana total become magically inert, and cannot use or control magic in any way — there is no other effect, so the only relevance of a negative mana total greater than -1 is to determine how long it will take before it is restored if Drained below zero.