First reactions after finishing the book? MARSH LIVED!
first up, I think the earring Wax has did not contain any trace of hemulurgic charge, Harmony/Sazed would probably not adopt any of ruins bad habbits. Despite it being used as a way of communication it is probably nothing more then an antenna. This can be noted in that ruin could effect peoples decisions despite them not having a spike such as Vin's mother and persuading Zane to stab himself despite most people thinking such a thing would kill and the hardest evidence is ruins ability to manipulate metalmind memories, therefore Ati certainly can play with the mind as can Sazed. Presumably because each human contains a bit of ruin and preservation so it should be possible that the two shards can commune with the missing parts of itself. Much like the preservation ghost mist figure appearing.
Second. The book Marsh gave, didn't spook have a book at the end of HOA with the letter? my bets are that its the same book. And it is probably a sort of wikipedia of scadrial, possibley containing the knowledge sazed gained from becoming harmony. Other Shards?
Third. The Kandra most likely all work for harmony, and those who don't are probably kept watch on by sazed. And that Harmony replaced somone to possibly help Wax a bit like a certain Mistborn and wolf?
Fourth. The Obligators if they did perhaps look over contracts and business meetings would of been in attendance to Wax's marriage contract.
Fifth. The Set cannot steal power through hemulurgy without harmony knowing, so they cannot create Inquisitors and even if they did the Inquisitor would be in Harmony's power like Marsh. SO their only real Hope is to create a mistborn, however this will take a long long time.
Hence I believe they were stealing these young women to power something else all together. Perhaps just to bank roll thier operations in discovering the true way to make a mistborn? Lerasium.
In a world with a large amount of twinborns, a normal mistborn would have difficulty taking on two or three twinborns. Think Kel vs Inquisitor, it was a tough fight however if Kel's allomantic strength was on par with Elend who took Lerasium we can see that the Mistborn would come out on top, but it was still a tough fight.
Sixth and final I promise! I feel that Harmony is concerned because of the conflict caused by the Set, it would make sense with BS liking to swap roles such as in warbreaker. We can presume that the Set is like the Anti-kelsier Crew. Wanting to take down the leaders of Elendel with a small crew of Crack allomancers and Larasium is their "16th metal" opposed to Kelsiers "11th Metal" Now all we know of the "God" metals are, that they do not exist anymore. Presumably as Atium was burnt up at the climax of HoA and Elend taking the last bead of Larasium. However also in HoA Vin absorbs the body of presevation (the mist) and it is seen once again by Wax, so it can be presumed in 300 years perhaps the Pits of Hathsin and the Well of Acension are pumping out the bodies of their respective deities. And thus Harmonies concern that another War may take place. And that a rougue Kandra may give away the location of Atium. And yes I know the Pits were destroyed, but perhaps Harmony rebuilt them for some reason. This may also co-inside with the canto of cartography marking the centre of Elendle with the Larasium icon as, the line probably travels over the location of the Well. Plus the iron each side probably denote the location of were each metal can be found in the province. As it was mention that Luthadel/Elendel were built on reasource rich soil.
Sorry about the essay!!