I think that be a great idea. Rewarding the members for the weekly challenge with SG reward system and at the end of the month the top member from the 4 gets the electrum reward to top it.
What does "top member from the 4" mean exactly?
If I understood correctly, that would be confusing because there is weekly and monthly reward for the same thing. Why not just make it more simple?
(small) Weekly Challenge -> runs for one week after which the winner gets an award icon
and..
(big) Monthly Challenge -> runs for one month after which the winner gets an award icon AND electrum