Whether you're going to be doing Trial of the Crusader on 10 or 25 man mode, you need to make sure that your raid is very balanced. Healers should be a mix of direct, AoE, and HoT, tanks need to be well geared with high stamina, high armor, and good avoidance, and DPS needs to be about 50/50 ranged and melee.
For 10-man mode you need 2 tanks, 2-3 healers, and 5-6 DPS that is half melee and half ranged.
For 25-man mode you need 2-3 tanks, 5-6 healers, and 16-18 DPS that is half melee and half ranged.
The difficulty level of the ToC normal modes is around the same level as Naxxramas on technicality, and just above Ulduar on boss HP, incoming damage, and healing required.
The heroic modes, however, are exponentially harder. While most groups can easily PuG both 10 and 25-man modes of Trial of the Crusader, pugging even a couple of spots in the heroic modes is not advised. In fact, having anyone one the raid who isn't at the pinnacle of skill and gear is not advised. The fights aren't technically difficult, but even the slightest mistake can lead to complete failure. So, with that out of the way, let's get onto the fights and strategies.
The first "boss" in Trial of the Crusader is actually three bosses strung together. Each one of the bosses is a "beast", therefore the set is referred to as the Beasts of Northrend. Only after defeating all three in a row will you receive any loot. On normal mode the next boss will only come out once you've defeated the one before it, but on heroic modes you have a set amount of time to defeat each one, and the next will be released ready or not. It is worth mentioning that on both difficulty modes you will stay in combat throughout all three bosses, so don't count on being able to drink between them.
The three bosses are summarized as follows:
Gormok the Impaler - Heavy Melee and Bleed attack boss. Requires tank swapping. Some adds. Fire.
Acidmaw and Dreadscale - Two bosses, can be burned one at a time or together. Raid spread out. Front breath and tail sweep. Coordinate debuffs.
Icehowl - Tank and spank, with moments of epic running away. AoE freezing breath randomly targetted.