There have been a lot of suggestions for exchanging energy for potions through the black spirit. Another suggestion could be to exchange energy for potions through the exchange currency tab to do your total energy over all of your characters in one go. There are too many boss alts to bring back to exchange them all in a reasonable time. 

This change is absolutely needed. It would reduce stress on the server.

But most importantly, avoid crashes. 

I agree with the system you proposed, a bag that contains all the energy of the characters to decide whether to use it themselves or exchange it for potions to sell at the market.