If the coins can't get through wood, then they can't get through plate. Warforms, who are easily as strong as someone with pewter, thrust pikes into Jasnah with no effect. Regualr steel plate can defeclt arrows from 160 pound bows from ten paces.
Wax could only possibly do it in one shot. It would still take him 2-3 on average.
They use three gems at most, so no they don't use a lot of stormlight. We saw them make an entire building. Kazah made a whole in one of the stone spires around Aiamia large enough to sail a ship through.
Hm, I suppose that might be possible. Make the illusion bigger, so it's a black sphere ten feet in diameter, with the Mistborn at the center, they will never be able to touch it, and thus can't leech it.
Unclear.
What's to stop the radiant from following the Mistborn everywhere?
The average Mistborn only had ten metals.
It's not exponential, it's multiplicative. TLR is FAR more powerful than any other allomancer we've seen, his compounding is thus far more powerful as well. By the time a Mistborn is alive at the same time as medallions Radiants will have plenty of surge fabrials.
And it's not a week it's weeks. So a minimum of 2-3. Even with Duralumin it would take you at least a month to get a bracer full enough to even resist a shardblade.
Leeching can't go through or affect plate.
Spren predate the arrival of shards on Roshar.