My Ideas:
CCS-class
Role: Long Range Heavy Cruiser
Ability1: Precision Strike
Description: Shipmaster orders vessel to fire a pair of low charged precision shots slowing down engine speed and increasing weapon cool downs.
Ability2: Huragok Engineering
Description: Ship shuts down weapon systems and engines to enter a rapid repair and recharge cycle.
CPV-class
Role: Short Range Heavy Cruiser
Ability1: Broadside Cannons
Description: All power is diverted to close range weapons increasing its combat effectiveness inside a certain radius.
CRS-class
Role: Light Cruiser/ Vanguard
Ability1: Screens enemy warships taking shots meant for larger vessels.
CAS-class
Role: Flagship (Could also be a Titan)
Ability1: Test of Faith
Description: All power is diverted to weapons and shields for a push through enemy lines.
Ability2: Invasion
Description: Lauches a Phantom dropship swarm (similar to what you see at the start of Halo 4).
Ability3: Covenant Battlenet
Description: Fleet Commander taps into the battle net delivering a rallying cry though out the gravity well increasing performance in battle.
Ability4: Slipspace Grid
Description: A High Councilor has boarded to oversee the fleet, the safety of this individual is paramount and as a result we have access to the slipspace grid to call in reinforcements from anywhere in this sector.
CSV-class battleship: (Should be at least as long as the CAS if Titan)
Ability1: Full barrage
Description: Fires a multiple barrages at enemy warships.
Ability2: Sermon
Description: A Hierarch's (or Arbiter if Elites are chosen) delivers his sermon (speech) though out the gravity well increasing effectiveness of our forces.
Ability3: Forerunner armor
Description: Further examination of reliquaries and the Forerunner Dreadnought at High Charity has given us greater understanding of our Lord's designs.
Ability4: Slipspace stabilizer
Description: (Maybe a returning armada esq ability can be used with this.)
Ability5: Plasma Lance
Description: Human engineering (Elites) Forerunner engineering (Covie Remnant) has lead to a powerful new weapon.
Ability6: Stasis Enfolder System (mentioned in Halo 4: Encyclopedia, no idea what it actually does)
Description: Freeze units within a certain radius.