Cannon - good range, devistating if it hits right, slim chance it will explode on you
Organ Gun - mediocre range, can kill up to ten models at a time, auto hits, slight chance it will explode, this is your skirmish killer
flame cannon - decent range, good against flamable targets, slight chance of explosion
bolt thrower - decent range, fairly accurate (if your Balistics is up to it) armor penetrating, this is your cavalry/WoC killer! Place them on your flanks to get as many flank shots on cav as you can. If I take them I always take three, one on each flank and one dead center.
Did I miss anything? Gyro copter's not really a war machine, it's more of a monster IMO.
As for the infamous "slow moving" don't forget that once you are within 8" of your opponent you will be the only one able to march. That will make you faster then him on the ground, though he will still have a better charge distance. As for ogres on the charge, who cares, they kill a couple dwarfs, you ignore the losses and procede to crush them with scr.
Finally on the ranged unit tactics.
I don't care which unit you take, thunderers or quarelers, it mostly depends on what your enemy has, either way you can't move and fire. If your opponent has anything to say about it he will not let you have a hill to fire from and that's ok. What you can / should do in that case is set your ranged units as your front line, aprox 3" in front of the rest of your troops. Keep long beards interspersed throughout your line. Let the enemy advance under a hail of fire and once they finally do charge you, well, stand and shoot if it seems worthwhile (a dwarf ranged unit is still the equal of many other armies infantry) or better yet flee, the 3" gap ensures that there is only a 1:12 chance of your unit getting cought and makes the enemy very likely to fail their charge. The long beards themselves are immune to the panic checks you just caused and provide the rest of your line with a good bonus to ignore them also. Finally, your dwarven leadership should be more than sufficient to rally the fleeing missile troops while your heavy infantry carves up the enemy with a charge of their own following the failed charge.
Down side to this tactic is that if the enemy is also a ranged fighter and you set up blind you will be very hard pressed to reform the line to make yourself usefull. Pray it never happens as nothing suffers against a dwarven guline quite as much as a dwarven infantry line.
More than anything else, have fun with it. I wish you the best of luck.
C'mon, Click my Daemon. You know you want to.