FFA's are rare...most of the one's I've seen are open only to friends of the host...
4v4s and 5v5s are pretty much it...and you really really have to be comfortable with fast and faster game speed...
It's the game speed that really kills me, and is the single biggest reason I hardly play on ICO...all my SP and LAN MP games are on normal speed, and transitioning is hard...I don't use the empire tree at all, and I don't use keyboard shortcuts...works on normal speed, not so good on faster speed...furthermore, faster game speeds favor early fleets with more capital ships and more vertical expansion...so, just make sure you're prepared when you go on ICO...