There is no maximum per map size, to my knowledge.  There is a hard coded limit that is about 100 total players.  There is probably a defacto limit on smaller maps since 100 homeworlds won't fit.  Are you really looking for more than that?

I can confirm that every galaxy size has a maximum number of players that is allowed.  The number is different for each galaxy size.  It is possible to go higher than that, but the game won't  allow you to leave the setup window until you reduce the number to an allowed value.

I haven't found these limits anywhere in the xml files.  I'm not sure if that means I missed them or if they are hard coded somewhere else.

Also, this is Intrigue.

Here are the player limits in Intrigue and probably in any version of 3.0.  I don't know if the amount of RAM changes any of this.  I'm on my laptop with 16 GB of RAM.  I'll try my desktop with 32 GB of RAM later.

It is not possible to go above the Maximum number of players.  Since you are a player, the number of opponents is one less than the maximum.