This idea is very curious to me. As others have said, I like using the RAW to build things as opposed to making up things House Ruled all the time. So here's my take...
Two thoughts to begin help...
#1.
A similar (in idea - creating a group of "helpers") power DUPLICATION is not scalable to Cosmic Power levels. So I'd wonder if Summoning is limited to not being a Cosmic Power as well?
#2.
But the RAW states: Scaling Powers to Cosmic Levels - "Most powers that are scalable to Cosmic levels, you simply continue applying the existing rules beyond 5 levels." (BASH! US p.95)
So... let's look at the key existing rules that we could "continue applying" for Summoning.
SUMMONING
1-5 pts; Concentration
This power enables the user to call living things into being, or to bring non-living things to life.
The summoned being will have points in powers equal to the user’s level in Summoning.
(with a maximum of 5 in each stat and a minimum of 1)
This rule is cut and dry. No change. Simply: Power Points to spend = Summoning Level. Easy. Though you might use the Enhancement (noted below) for "Extra Effect" to allow stats above 5 for Cosmics.
Stat pool equal to the user’s level in the power +2.
Again, this rule is cut and dry. No change. Simply: Stat Points to spend = Summoning Level x2. Easy.
All have identical stats and powers.
A summoned being cannot have the following powers: Healing, Duplication, Shape-Shifting, X-Ray Vision, ESP, Telepathy, Mind Control, Clairvoyance, or Summoning/Animation.
All can move each page.
Only one can act each page.
All simple, cut and dry.
You can summon:
One Creature @ 60 hits
Two Creatures @ 30 hits each
Three Creatures @ 20 hits each
Six Creatures @ 10 hits each
Here's the sticking point with your "army" idea... And where I impasse with urbwar's extension of the rule according to the RAW.
At nowhere does it say a Summoner can create 4 or 5, or 7 or more Creatures. Period. There is no suggestion that the rule "extends" beyond Six Creatures the HITS would also be assumed to lower with each stage. I don't think the idea is to allow this at all.
With that...
Perhaps, to achieve the "army" you're looking for (great idea BTW)... and still trying to follow the RAW - I might suggest considering what this enhancement might be able to do, it's "rule" is sort of nebulous so it might be usable to "upgrade" Summoning to the Cosmic Style you want:
ENHANCEMENT - Extra Effect: This enhancement makes the power more effective in certain situations.
In the case of non-damaging effects, if no multiplier is involved, then duration might be doubled in that situation, or alternatively, the Narrator and player can figure it out together.
Perhaps making the Extra Effect double, but this still wouldnot take it into "army" category really. Unless you took the same "Extra Effect" multiple times - which would square the total each time. Something like:
Extra Effect 1 = 12 Creatures @ 10 hits each.
Extra Effect 2 = 24 Creatures @ 10 hits each.
Extra Effect 3 = 48 Creatures @ 10 hits each.
Extra Effect 4 = 96 Creatures @ 10 hits each.
Extra Effect 5 = 192 Creatures @ 10 hits each.
Extra Effect 6 = 384 Creatures @ 10 hits each.
Extra Effect 7 = 768 Creatures @ 10 hits each.
Extra Effect 8 = 1,536 Creatures @ 10 hits each.
Extra Effect 9 = 3,072 Creatures @ 10 hits each.
Extra Effect 10 = 6,144 Creatures @ 10 hits each.
Extra Effect 11 = 12,288 Creatures @ 10 hits each.
etc...
Alternatively. The only other way I can see that you might do what you're looking for:
LIFE:
Look at using the Cosmic Power "LIFE", as it utilizes Summoning as part of it's base power. Though it does not suggest being able to increase the actual number of Summoned Creatures - exactly the same problem the base Summoning has and it notes that LIFE is different than Summoning, in that the summoned are "real"...
OR
Use the Villain Advantage (BASH! p.67)
Devoted Henchmen
This Villain has an army of loyal minions, who would even die for their master. A Villain with the Devoted Henchmen advantage can use them to give himself a Dice Bonus on attacks, as if they were assisting him on a skill check. In addition, whenever this Villain is hit by an attack, the Villain can spend a Setback to make one of the minions take the hit instead. Devoted henchmen are often robots, undead, animals, brainwashed, etc.
Perhaps with a combination of:
Sidekick to have a "Captain" of the army, or the like.
Whew.... that's a toughy. I'd love to hear BASHMAN's ideas for it...