On a 120 build fleet I have 2 type, my carrier fleet and my battleship fleet. The backbone of my Carrier fleet are always 2 or 3 carrier ship, depend of the size and for the Secutor who I consider like a super-carrier I bring just one . I keep those behind with some escort carrier between 2 or 4 and with an interdictor.
My attack group have 3 capital ship like battleship or battle\heavy cruiser(ISD\Dauntless). 3-4 escort like strong cruiser (Reclusent\Mc-40). 3-4 light escort like frigate or corvette(Nebulon\Correlian). So that make a ratio of 1-1-1 or 2 escort for 1 capital ship.
In the middle I keep some long range\torpedo like Marauder and Victory.
That my carrier fleet I keep mostly for defense and I keep 3 fleet like these.
I like to have 1 or 2 battleship fleet. Whit the lvl 3 ship. ISD\Mon Calamari\Invincible. I have 3 of tank type my favorite it the Alliegance or the Tector or the Home One type. Those big one I can bring only 1-2 but I like to have 3, that make the backbone. In total in my battleship flleet I have 5-6 capital ship, 2 or 3 of each type the faction have. Like Tank and Dps. Each one need a good escort cruiser and probably 2 for the big one like Allegiance.
I bring some escort cruiser and an Interdictor. I take some light frigate or corvette to escort the fighter, like 2-3 nebulon and some gunship not more than 6.
I fill the rest if Im able with long range\torpedo or cannon fodder\front line like the gladiator or the dreadnought. I can sometime go a little over 120 because those are my attack fleet so I can choose what Im sending but that not my main fleet so it go a little over just to have a good ratio of Capital-Ship\escort.
Finally I make a main fleet the only one with over 120, with the biggest ship and the best heroes SSD if available.
Example of my on going campaign with Corporation;
Carrier-
3 Lucrehulk
3 Dauntless
4 Recusant
3 Quasar
2 Nebulon
1 Gozanti
1 CC-7700
Battleship-(I didnt find a good ratio for them yet)
2-3 Bulkward
2-3 Invincible
2 Victory type 1
3-4 Quasar
1 CC-7700
Goazanti\Nebulon or Marauder or a mix.
I can bring some Dreadnough, Gladiator and Neutron.

Corporation are a bit special because they dont have SSD type so I keep only one battleship fleet as my main fleet. Lucrehulk make a pretty good planet defense ship so I will use mostly just the Carrier fleet as defense in key planet of some Sectors. My main fleet will cripple the AI who lead on the leaderboard and dont let anyone take avantage on the other AI and trying to let them fight a little between them without open unwanted front for nothing.
Normaly my 3-Carrier fleet defend key planets and my 2 battleship fleet counter attack. My main fleet go on rampage with my main invader ground troop. Conquering a sector at the time leaving blocking space of 4-5 planet at the time and then invading them one by one. I simulate all my ground combat so I cant really conquer more thant 4-5 planet at the time. It leave time to make the best planet as some sort of strong point.

if you are playing as greater malrood, the alliegence battlecruiser is an amaxing ship. very few ships can take it on in a 1v1 or even 1v2, its main issue is its fighter and corvette weakness. it has no fighter bay and the guns feel clumsy, therefore its amazing to take on capital ships and cruisers, but needs to be supported by a few carries and corvettes to hold off fighters. if used correctly it is by far the most powerful ship for its pop count, but if unsupported it becomes the worst.

Need some Empire of the Hand Builds

I play Pentastar Religiously and this is mine:
1-2 Secutors
4 ISD IIs
2 ISD Is
2 Victory Is
3 Venators
6 Vindicators
3-4 Enforcers
10 Raiders
2-3 Carracks
2 Dreadnaughts
1 Immobilizer
4-5 Arquintins (can't remember if these are still Pentastar)
4-5 Acclamators

What I drop in is dependent on what I'm fighting. Sometimes I use the support ships as hunter groups to attack vulnerable carriers, but this comp is mostly suited to building a very tight formation to break enemy attacks on.

Wait can we make fleet compasitions of units from multiple rosters?

I play mostly New Republic and i think i figured universal defense/offense configuration, at least it works for me on medium difficulty GC.
Era1-2: 5xMC80b + 7xDauntless + 4xCR90
Era3: 5xMC90 + 5xDauntless + 5xCR90 + 5xSacheen
Era4-5: 3xNebula + 1xEndurance + 5xBothan Assault Cruisers + CR90/Corona
Add Golan Defense Platforms,Empress station and Ion Cannon support and they handle anything from usual ISDs to Allegiances and Executors.
My offense tactic on Era1-3 is :divide and conquer" drop advance CR90 for recon, assess enemy fleet composition, drop "bait" ships to the edges of map, wait for enemy to break formation and deal with smaler groups with tactical drops. If opponent has small fleet but you want to take them out fast and hard, then it's "shock and awe" time drop every ship right in front of them and interdictor to hang back and block escape.