Is there a limit to the number of fleets/ships you can support? I'm generally hesitant of 4x strats that support amassing super fleets. It devolves the gameplay in my opinion and makes it hard to pursue other victory conditions. Sword of the Stars II, for all of its failings, does do fleet management well. Your number of fleets is limited by available admirals and fleet size is limited to your command ship class. Does Endless Space have something similar?

No limit fleet (for the moment)!

There's no limit on the number of fleets you can have, afaik, but there's a hard limit on the size of individual fleets. You can raise that limit through tech, but it's always capped.

The size of each fleet is limited by your number of command points.

OTOH there is no limit to the number of such fleets you might have... But you have an upkeep running each turn, so you need to watch out.

Admirals are heroes and the number of heroes ingame is severely limited (3 at beginning, with 5 more you can get provided you have the right techs.)

So usually, you have 1-2 fleets with a hero helping, the rest without.

I seem to recall reading that upkeep costs ramp up, making massing to obscene levels counterproductive.