First of all, more information if you let us:
0. Besides the obvious eastern pass, are the two other paths (ones without roads and that appear to have some bodies of water in them, north of Black-Briar Lodge and south of Forelhost) passable by armies?
1. How much actual "authority" do we have over the Stormcloak defensive effort, bearing in mind that we are acting through proxies such as Maven? Is something like paragraphs 1 and 3 of my last post actually doable or are we limited to going after the 6 assets you outlined?
2. Ask the Maester what he knows about the local orc tribe. Do they have strong feelings one way or another over who rules Riften? Is there a substantial population of legionary veterans living there? What motivates them and what could motivate them to back an action against the Westerosi and/or Stormcloaks?
3. Ask the Maester about the Dawnguard. Are they the type to burn the learned men as witches or do they have respect for them? Do they mistrust the gov'ment as a proper right wing militia does or would they be open to cooperate with the Imperials? Any weaknesses, strengths, quirks, opportunities, etc? Also ask if there are any recent events that match their mythos that can be used for influence/fearmongering.
4. Ask the Maester about the Dorklight Tower. Specifically about how its place in the local mythos can be used for influence/fearmongering.
First steps (to be revised if/when questions above are answered):
1. Launch plans as per par1&3 of my last post: conservative defensive strategy starting with the bridge and retreating into the pass, with frequent sorties etc. Since we have 200 cavalry, perhaps send as much as 50 light horse for the latter purpose.
2. Send a Stormcloak messenger to Kai Wet-Pommel and try to recall him back to Riften. Overemphasize the Westerosi threat and that the cloaks cannot afford to lose another city, the Imperials be damned.
3. We together with Maester and one of the Occulati ride to Dayspring Canyon to parley with the Dawnguard. We show off the seal to explain that we are speaking with Imperial authority explain that there is a Westerosi force heading our way. Explain that King Robert is a tyrant who will certainly not tolerate independent armed groups such as the Dawnguard to operate in his realm and that therefore this is an existential fight for them as well as for the Empire. Promise to make give the Dawnguard official standing as Imperial Witch Hunters and given the full support and cooperation of Occulati intelligence network when Riften is in Imperial hands. Have them stay put until activated - maybe set up some sort of signal or swap information.
4. Meanwhile, send the other Occulati agent to the local orc tribe to parley. Somewhat stupid and cowardly? Try to sell them on the idea that Riften is about to be
very weak and that, if Orcs help Empire attack it, they get first dibs on all the raping and pillaging. Maybe have the agent sell this idea to fellow veterans who would in turn sell it to the rest of the tribe?
5. Send a messenger to the Shield-Brethren and try to sell them on the threat of a Westerosi assault from the direction of Windhelm. Try to convince them to transition at least a thousand of their men to Mistwatch (this will hopefully safeguard us against a hypothetical attack from that direction while weakening the force stationed in that canyon)
6. Send the men to Faldar's Tooth. Getting flanked is for pussies.
Darklight Tower is obviously superstitious nonsense.
Abstracted long term plan: We help the Stormcloaks fight back the Westerosi but consolidate pro-Imperial assets (ideally consisting of legion remnant, orcs, Maven's criminal connections, Dawnguard, armed with the latter's tech) to mop-up and takeover or at least isolate Riften until a larger Imperial force gets here. Since I assume the city guard is on Maven's payroll, perhaps we can close the gates on the army in the final days of the siege (Visby, anyone?) and force the Westerosi and Stormcloaks into an open battle outside, then mop up with our assets? We'll see, I guess.
Anyone have criticism or ideas?
Grimgravy ?