My friends and are going to meet up soon and I am thinking of getting Castle Crashers on steam. We already have enough controllers for 4 player, but I am wondering if we will be able to all use them. Assuming there are enough USB ports for a wired connection, can Steam, Windows, and Castle Crashers handle that many wired controllers?
Windows and Steam do support 4 Controllers (regardless if they are wired or not).
Doubtful, however, is if Castle Crashers does. In the Steam dicussions to the game ( e.g. here) there are both people who have success with playing with mutliple controllers and people who failed in trying this.
The player from the above link apparently got it to work by plugging in the controllers after having gone to the character selection.
Another alternative is to install an additional software such as xpadder. xpadder allows the mapping of keyboard keys and mouse buttons to your controller. This would work with a high chance when Castle Crashes supports a 4man multiplayer anyway. xpadder is not freely purchaseable, but alternativeto.net delivers a lot of results for xpadder. Such programs also allow you to play games that are normally not playable with controller at all.