1) I want to disagree with you, Von Kurst, about the beastman thing, but I think you're right. The rules for TLGT say promoted henchmen retain their henchman type. A promoted Ghoul stays a Ghoul, and the rules for the Undead warband say, "Ghouls: Your warband may include any number of Ghouls." Ok, bad example, but you get the idea when it comes to limited henchmen types.
2) The rules for charging require that models declaring a charge be able to draw an "unobstructed line from your model to the target." This will technically be possible 99% of the time because it doesn't specify that the line go directly to the target nor limit the length of the line in any way.
The rules also state that a charging warrior must move by the most direct route into base to base contact with their target. This means you can't do things like charge in wide circles to avoid intervening models or terrain.
There are, however, rules for charging a model that can't be seen. If a model is within 4" of an enemy (remember you can't measure before you declare a charge!) that it can't see, but isn't hidden, you must pass an initiative test to charge the target. You still have to move via the most direct route. This means hugging corners; and enemy models for that matter. Seems like you could charge around enemies if you're within 4" of the model you actually want to charge and can pass an initiative test, but you must pass as close as legally possible to the enemy models (1" away for standing, unengaged models) while measuring the distance of the path of the charge (not the direct distance to the target) to make sure the charger can actually charge that far.
Which brings the charger right into intercept range. If the charge path passes within a 2" radius of any enemy models, the charge may be intercepted by a single one of those models (provided the model trying to intercept isn't in combat or knocked down or something).
The rule book actually fails to define the action of an "intercept" at all, telling us only about conditions surrounding it. It mentions that the original charging model still counts as charging and the intercepting model does not, implying intercepting places the charger and interceptor in close combat. It doesn't say whether the interceptor moves into the path of the charging model, or if the charge simply redirects to the interceptor, or even if the charger remains still and the interceptor is moved all the way to the charger (which is pretty ridiculous). You're on your own for this one.
So basically, if you think models block LOS the Skaven player probably shouldn't be allowed to charge models behind other models, unless they qualify under the rules for charging models that can't be seen. Otherwise make sure they're charging along the most direct path, and intercept them if possible (whatever intercepting actually is). No gerrymandering charge paths!
3) According to the rules as written blunderbuss can shoot into close combat and, technically, even through walls. It just says you draw a straight line ye long and ye wide and models touched by the line are hit.