The definition of ultimate is quite relative anyway, here are my ultimate stacks :
Portugal : (upkeep)
1 X General (250)
4 X Musketeers (600)
4 X Dismounted Conquistadores (600)
2 X Conquistadores (500)
7 X Adventuros (1295)
2 X Basilik (800)
= Total upkeep of 4045 per turn

Milan :
1 X General (250)
4 X Italian Cavalry Militia (600)
6 X Genoese Crossbow Militia (600)
9 X Italian Spear Militia (1075)
= Total upkeep of 2525 per turn.

So you could have allmost 2 milaneese armies on the field for 1 portuguese, and this is not counting the purchase price, the building requirements (and the events requirements) and the impossibility to retrain.
Technicaly the milaneese stack can be made with a merchant's guild and the first stone wall level.