^Two of your cons can be taken out if we got to what had been a small city 12 years ago: Weistgren.
Warg himself said that this could have grown into a town already due the quickly growth of Halme population when they live good and safe. And that small town had back then already a wall and xx smokes coming out of their smokestacks so they got enough coal/wood to survive the Winter as well as to create own armor/weapons for a little army to protect themselves.
We have seen Halmes in armor and weapons, one even sitting on a mount, when we were on the road to Weistgren! They could become a valuable surface battle partner if they got more mounts/Halmes who has warrior equipment and knows how to fight. What the Dvergar are in the underground, the Halmes/Kotorcs could be on the surface. Especially since they got bigger numbers than Dvergar or Drows put together.
Also we can trade Mounts much cheaper with them using the gold bars/silver bars from the Dvergar we get for some meat/fish/glass/wood items whereas Nals would want either lots of items or even ada in return. And the ada could be used better to purchase books, more mana plants to increase mana pool, buy a teacher to get over his worries with LOTS of ada we saved over time, etc.
And depending if the Halmes are at a sea or an ocean they could have a port, trading with other countries like the Emberi are from: Exoctic items could get easily brought by us for some gold pieces (if we do a currency with it besides ada/silver) which can be sold for lots of ada in Chel and other cities. Since the Nals got an easier access over us and we an easier access over the Halme port, the other clan´s traders can´t competent with us and our prices. They will have to sell really low comapred to their costs and efforts which will leave the exotic item trading field in a few years to our Halme->Us->Nal trader route.
So yeah, there are quite some stuff that could prove helpful getting them on our side. Just like the dvergar proved to have access to SALT. And not only that but also metals whicha re useless to us, but very helpful to get the Halmes on our sides: GOLD and SILVER.
Even after we make those little gifts for Mirual, Orrul and Ruiuff there will be still left enough to get a couple mounts/farm animals when we visit them for the first time which will grant us their interest and their hope we return again with more gold/silver.
Once we have them besides the Dvergar on our side, it would be time for creating our own currency in Ada (for Drow/Dvergar interesting), Gold and Silver (for Halmes/Kotorcs (Herminones too)) interesting.
I think its worth a try to get there though i dunno we should start it when we got 14 people out in expeditions next week and the 3x people at the campign have not returned either. Maybe once those two ended/the War group´s back we can do so.