Lovely.
What kind of soliders do they come with? What materials will they use? Do humans use mounts? Do they announce a siege, or do they sneak up like elves?
Humans can bring any type of soldiers. Scourges are the only weapon they don't have access to.
They can be mounted on common domestic mounts, which generally makes them harmless, because those mounts are all [BENIGN]. Mounted archers, on the other hand, are extremely dangerous because of this.
They may be armed and half-armored (Helm/cap+mail shirt/breastplate/leather armor + shield) in bronze. Iron, copper and silver too if they have access.
Dwarves have no bowmen nor lashers nor pikemen. They are limited in their choice of weapons to what you can make in fortress mode.
I never seen them mounted on anything, but that's most likely just me and they'll most likely come mounted on cave animals someday.
They can bring armor and weapons made from anything. Raw metal gear is possible only if their civ has access to it, while alloys (including steel) will be present in any case.
regarding slade, they will not have it if it is smelt from slade ore, because they have no access to slade stones. If it's an alloy, they'll have it.
It would also be a good idea to check legends mode to find out what unusual animals have your enemies tamed. Humans law-givers and dwarven generals sometimes may tame something you'd better not see attacking you, like war giant tigers or giant eagles or jabberers or giant cave spiders.