I always use mixed squads. for starters its probably several years before you can spare and armor even 4x5 dwarf squads, add to that the fact that most of the first 2 migrant waves (non-historical) probably dont contain much military goodness means i start mine slow. Mix anyone worthwhile into a squad and let em pick themselves. Once theyve decided i usually do a quick check to make sure im not completely imbalanced.
A couple of blunts are a must have, they are your best chance vs an inorganic monster (minerals, metals) and also vs anything very heavily armored (steel/iron, though i dont beleieve any vanilla mobs use steel). New undead demand blunt attention too.
Axe is the ultimate limb remover, goblins only armor the torso and head usually so axes take care of the rest.
Spear is vital, you always need a spear. For a soft target that is too large for an axe to remove a limb (MB/FB/Titan) then a spear is your friend, organ shots can bleed it out while axes hack at fat layers.
Sword as mentioned is a crossover, weak axe and weak spear joined. good default weapon for majority of troopers, covers 2 roles.
You could probably get away using only swords with a squad of blunt somewhere to put down the specific targets that require them. In reality i send mixed units, there are some occasions where they mixes cooperate well, perhaps a troll is too fat and the axeguy cant remove his leg, np, spearguy sticks him in the gut, causes a passout and the axeguy takes the head instead.
Wrestlers are also theoretically strong mixed with other troops. The idea is that through use of holds they immobilise enemies for their squadmates to kill. In reality you need a good wrestler for this, and most dont survive their first engagement, let alone progress to gain serious skill.
Edit: Also, nothing wrong with crossbows in your melee units. just be sure to give them a second weapon so that they dont crossbow bash. since they train hammerdwarf anyway give them a hammer and they will swing that instead of xbow when they find themselves in melee, and even be rather good at it.