Guys, this is really important. Supporting the marshal's initiative is a massive mistake. He is stronger than the Emperor (just compare their descriptions), he is more popular than him, and he is asking for us to strengthen a legion stationed around the Imperial Capital. This has "military coup" written all over it. I am not an ancient history buff, but I am pretty sure that Roman history was full of cases where generals with more public support and military power than the emperor attempted to take over. The Dominion is a real threat, but this enemy is closer to us than the elves are.
Also, Runa (or rather, her patron) scares the shit out of me. I am betting that this is work of Varys. His probing worked, now the ball is in his court. Not good.
So,
1B - why would we reveal our strengths to a potential coupist? This is stupid. Let's continue to pretend that we are the Emperor's clueless buttboy.
2A - rejection might mean that he will go to someone else with this plan. That would be a bad thing.
3D - we must make it so that the plan is impossible. Whether it is going to be shut down by the Emperor or simply slowed down with red tape, we will at least be able to postpone the marshal's plan.
4E - our inability to deal with Runa proved that we don't quite have the powers of subterfuge on our side. We need Varys' respect and support, and that will allow us to have leverage with the other members of the court. And if he was the one who sent Runa, that means that perhaps he will cease with his attempts to spy on us, or at least be less inclined to manipulate us.
Hopefully our maid's spying will give us leverage over the master of keys, so we don't need to worry about cozying up to him as much.
Tamriel isn't the worst fantasy setting, to be honest. The plots of the games are terrible because nuBethesda can't write for shit, but the lore isn't all that bad. AFAIK most of it was written in the Morrowind days, when they had a few talented authors on board, but I could be wrong about that. And MercantileInterest's changes seem to be pretty monocled so far.