1. Divide the fleet into smaller fleets of the same types, eg. Fleet of 20 Sentinels, Fleet of 20 Enforcers etc. Is this better than a composition of many different types?
Late-game as Vasari, I generally keep one unified fighting force, and split it up on a strictly-as-needed basis. I use phase stabilizers to quickly deploy and redeploy this force.
I generally don't maintain static groups as any faction, instead building units as I need them and moving them around to where they're needed.
2. Ratio of Fighters/Bombers should be 25/75 or even more bombers simply to wipe out the large crafts (if they have many).
Yup; bombers are definitely the stronger of the strike craft. Fighters aren't useless, but if the enemy has large numbers of flak they will be killed very quickly.
3. The best capital ships to have in the fleet would be the Evacuator and Carrier simply because of their abilities. Maybe a few Devastators directly in battle along with Enforcers?
The Skirantra Carrier is definitely the best Vasari capital ship. The Kortul Devastator and the Jarrasul Evacuator are also quite fine. The Vulkoras Desolator is basically a heavily armoured siege frigate that can be safely used mid-battle due to its superior durability. The Vulkoras is a little niche, but if you want in-combat bombardment it's worth your time. The Antorak Marauder is very niche. Not completely worthless, but I've never found a use for it in multiplayer. It's level 6 ability is very good, but one ability that you might never actually reach doesn't carry a capital ship.
In my opinion, the Marauder is the worst capital ship in the game (with the TEC's Dunov a close second).
4. Take out enemy capital ships first, their support cruisers second and finally the rest of their fleet?
Depends on a lot of factors. Sometimes you'll want to knock out the units first, other times the capital ships make sense, and still other times the support cruisers make sense. It really depends on too many factors to simply give you a one-size-fits-all approach here.
5. Late-game, should you completely disregard Skirmishers? Are they replaced by Enforcers later on?
Not completely; Skirmishers have medium armour, which means they take very little damage from fighter and bombers. They're a great anti-carrier unit, and against someone who has lots of carriers with little backup they can make a lot of sense. They're also very fast and the only unit in the game that can outrun them is the scout, so they're great at chasing down enemies. Against an enemy who is doing hit and run attacks, a pack of Skirmishers is an excellent investment, and they can chase down virtually any unit.
Where they don't make sense is in a straight fight. They're not very good against heavy cruisers, and they're completely minced by long range frigates. So unless the enemy is making nothing but carriers and flaks, this unit type doesn't make much sense, and the Enforcer is a much better selection.
