I forgot a point. The various straits and canals have size limits.
NeoPanamax limits:
1200ft/366m long
168ft/51.25m abeam
50ft/15.2m draft
Suezmax limits:
1300ft/400m long
254ft/77m max, 164ft/50m at max draft
66ft/20.1m draft
223ft/68m height
Malaccamax limits:
1093ft/333m long
197ft/60m abeam
67ft/20.5m draft
So those make the real physical size limits on your ships.
Combined maxes:
1093ft/333m long
164ft/50m beam
50ft/15.2m draft
223ft/68m height above waterline
So you can't get
longer than a Ford,
but you could get wider and deeper if you needed to. The Ford's flight deck is roughly twice the beam, so assuming that holds true as a general design thing you could make a flight deck 20m wider than the Fords, and draw another 3m deeper. In addition, the top of the mast could be 25ft/8m higher for a longer radar horizon.
Ford class displaces 100k at full load, the box of LxBxD is 164k m3 for a fineness ratio of .61
Max box size is 253k m3 times fineness of .61 makes the "globalmax carrier" have a displacement of around 155k tons.
So there you go.
~155k tons with a flight deck 20m wider than a Ford-class is the absolute biggest you can get. Flight deck area of ~26,000m3, which is ~25% more flight deck than a Ford.
Thing is, a carrier like that has a L:B ratio of 6.66. That's relatively short and fat. The "beamy" Burke-class has a L:B of 7.65, and the stubby South Dakota class battleships had a L:B of 6.1. That means needing more horsepower for the same speed. Lots more power, actually, the Ford-class has a L:B of 8.15 and has ~260k horsepower for 30+ knots. The SoDaks had
11,000 more horsepower than the North Carolinas (same displacement, better L:B ratio)
and made less speed. Your globalmax carrier is going to need at least 450k horsepower, better install the equivalent of 4x A1B reactors!
Edit: I think the Nimitz/Ford size carrier is the sweet spot for "largest flight deck versus horsepower needed", but I haven't sat down and ground the numbers.