Is it possible to adjust how much ffame is needed for each champion to show up? I guess I'd like to delay them by about 20 fame + 50% fame, or something in that neighborhood.
If you open CoreGameEvents.XML, there are events named "GameEvent_Champion_#" (no quotes, and # is replaced by an arabic numeral). These events have a fame value which triggers them (look for the line that starts with <TriggerData>, and this is the amount of fame required for the champion; <TriggerStringData> is the line specifying the resource required, and <TriggerType> is the line specifying the way that the event is triggered). Edit that fame value and you can change when the champions appear.
I'd suggest that you create a backup copy of CoreGameEvents.XML before you do anything to it, just in case you break something through an editing error.
Also, is there any mod or similar that makes it so that the nationality you are affects what champions join? It feels kinda weird to be, say, Altarian, having a whole nation full of Altarians, and then none of my champions are... It'd be nice if at least one of the two offered matched your own race.
Not that I know of, though you could check the list of mods over in the modding forum.