MP
So first you should have a strong host if you would play with more than 3 players.At time i host for a 3 player game and i got isdn64k,there are only less problems,no laggs and we are in 1550 with some big worldwars.But best host of course would be cable,adsl,dsl and all that stuff for a good game.Players should have minimum modem56k,in my game theres one man with modem 56k,no probs.
Second i prefer only to play with versions same language.There are often in my MP time many crashes and tests with different language versions,especially reloading was always a big problem(dear deil,Björn,Kalvera and all the others).But thats not the problem of the players,its of course paradox problem,the patch seems not work with different versions in MP.
So max players for connection speed

if host)
isdn=max 3 players
cable or higher=max 6-7
the cause if all players got something like cable or higher,there would be a game by 8 possible,but which 8 players got continues time for playing,i got no probs with 3 players,we play every day.
playing with edited files is no prob.So if you you meant configuring scenario file for major countries,only host need this prepared file.All the other stuff like IGC or any other scenarios changing any files of EU should have installed by all MP players to avoid any crashes.
Spain is no problem,run them down with France or Turkey.
Wilhelm