... Harbaal has been in Lorkin for a year, it is Lerden, having succeeded his dead father as Overking, and Lerden is interested in loot, not territory. ... He's after the Silver Way caravan. He would prefer to go via Gardiren, but he is concerned about tangling with Noron
Ok, raiding for loot vs invading for conquest sort of makes a difference.
The Silver Way caravan, according to CGI canon, is actually several caravans that are spread throughout the summer, starting in late-spring. A lot of gold & silver ends up at Gardiren to pay for grain, but most of the choice booty goes to Tashal for the summer fair. Unless you have excellent intelligence on the itinerary of the most valuable caravan, that loot is gonna be a difficult moving target.
BTW, there's lots of other loot in Tashal, too - not sure if the Fur road caravans will have been affected by the Harbaalese at Lorkin, but at least the Salt Route & Genin Trail goods will also be at the market.
The grain destined to go up the Silver Way to Azadmere is stored somewhere over the winter, awaiting shipment. Mostly in/near Gardiren, but IMO there would also be some silos just downriver from Naniom at Uldien/Fisen/Shebra.
The King, court, most major nobility and a significant portion of Kaldor's knights will be at Olokand for the Chelebin Tourney.
The Plan: Be greedy! Wait until the caravans have hit town, then sack both Gardiren and Tashal and take it ALL!
Early on, send an advance team to build the boatyard camp at Lake Myen. Also, have a group of seagoing vessels ready to sail around to the Kald estuary for the escape.
The main army comes down the Fur road in early summer (bypassing Noron), and splits into 3 forces. One group goes to the Lake Myen camp to fill the boats. Second group goes east overland, crossing the Kald above the Rhu, across Noron's Way, crosses the Shem above Gardiren (bypassing the bridge), and gets ready to hit Gardiren from the north. The Third group advances down the Fur road towards Olokand in a feint designed to pin down all those knights & nobles at the Tourney.
Once Olokand is engaged, the First group boats down the Hemurin/Kald and takes Heru, cutting off Meselyneshire and securing boat access to the Shem. The Second group hits Gardiren, raiding the treasuries for gold, the silos for food supplies, and commandeering any river boats to help the next phase, which is marching south to join group One and sacking Tashal.
Tashal might be a problem, might not. Much of the Royal Guard is at Olokand, but the Chelmarch army is nearby and the Lady of Paladins is right there at Whyce, with a lot of their senior members there for the Ainlana Tournament & Tirannon. Also, Tashal is full of mercenary guards that have accompanied the trade caravans here and are awaiting the end of the fair to escort them home again. It has city walls, and the raiders do not have time for a siege. I guess it comes down to "how big is your army?"
Once the city has been sacked, or not, groups One & Two load the choice, portable loot onto the boats for a quick evac to Tuleme, where it can be transfered to the awaiting seagoing vessels. The army itself follows south on foot. If they have successfully pillaged enough rations, they can take the Salt Route to Geleme/Tuleme and avoid other Kaldoran forces. If not, maybe they have to pillage their way through Ternua/Kolorn/Jedes, I dunno. Back in the north, group Three disengages from Olokand and retreats up the Fur Road.
Step 3: Profit!
There's probably a ton of holes in this idea, but it was fun to think about.