Borderlands of Cormyr - OD&D / Chainmail game

The Borderlands of Cormyr - an old game that we have been running for 5 years is starting back up again! A few of the players are more interested in domain play, so we have been doing a lot of skirmishes & wargaming using the chainmail rules. Most men survived the last few battles with a goblin horde of over 600 goblins - they have returned, and many are now taking their hand at becoming adventurers! The party will likely consist of lower level players, perhaps with one or two higher levels, so it is a good time to start. The town of Tilverton, north-east of the Cormyr area in the Forgotten Realms world, has been besieged by goblins as of late. The party has just heard rumors of a goblin kingdom in the nearby Thunder Peak mountains, which is likely the source of all these attacks. There is also the feared Harondalbar dragon that has been laying siege to the stonelands and Cormyr settlements to the west - the party has decided best to leave him be for now, but perhaps there is more to the story than just goblins... The idea for the game will be to use Chainmail for the overworld encounters (i.e. battles with over 200 or so men), and OD&D or perhaps OSE or B/X for the dungeon delving. Once your characters become heroes or heroes -1 (level 3 fighter) your character becomes quite powerful and harder to kill, but characters will feel pretty fragile at lower levels. Expect a lot of deaths, but hopefully that can be avoided with ingenuity and some luck.