I'd go 5kg Bruce and 5+kg of chain (length depends on link size) and 10mm rope.
As for aux, I'd rather have enough faith in main engine not to rely on one.
I guess you would need the correct size & bracket to make it useable. I assume you would still steer with the main unit assuming staring hasn't broken), so you want it deep enough to be in the water below the hull, but not too low to get potentially swamped.
Rob