Immigration can't really be done via mod work, a cheap trick is to go into the continents file and make your capital province in North America and then go democracy/full reforms as usual to get regular immigration.
You can also move specific pops to specific places but its very buggy, I tried to move slaves from Louisiana to the Amazon and they ended up magically becoming Dixie Aristocrats. Use at your own risk.

any_country = {
	any_pop = {
		limit = {
			is_culture_group = germanic
		}
		random_list = {
			10 = {
				move_pop = 1632
			}

			90 = {

			}
		}
	}
}

Would give any Germanic pop in the world a 10% chance to be moved to province 1632, you can swap the conditions for just about anything say

1632 = {
	any_pop = {
		limit = {
			type = capitalist
		}
	move_pop = 71
	}
}

would move any capitalists from 1632 to 71.

cores are pretty simple, there's two main ways I go about it, province by province and country by country

1632 = {
	add_core = FRA
}

adds a French core to 1632

KOR = {
	all_cores = {
		add_core = FRA
	}
}

adds a French core to every province that has a Korean core. Both of those work regardless of who owns the province, you're supposed to be able to target other things like an entire state but I've had trouble getting that to work.

War is also pretty simple but there are some tricks, add_casus_belli adds a CB to the target against the country in scope, casus_belli adds a CB to the country in scope against the target and war starts a war

FRA = {
	add_casus_belli = {
        	target = BRZ
			type = conquest
			months = 36
	}
}
would give Brazil a conquest CB on France, if you don't specify the country in scope it'll just be against whoever is getting the event

FRA = {
	casus_belli = {
        	target = BRZ
			type = conquest
			months = 36
	}
}
on the other hand this would give France the CB against Brazil

war = {
	target = BRZ
	attacker_goal = {
		casus_belli = conquest
	}
	defender_goal = {
		casus_belli = status_quo
	}
	call_ally = yes
}

would directly start a war between the country in scope to conquer Brazil and have Brazil fighting for status quo while the aggressor calls in its allies

war = {
	attacker_goal = {
		casus_belli = conquest
	}
	call_ally = yes
}

and this is a neat trick, it'll start a war against a country that doesn't exist, while calling in the country's allies, the allies will join all wars the country is in as they usually do when answering a call to arms and the war against nobody ends instantly, letting you call people in to wars they wouldn't usually join.

and finally
end_war = BRZ
would end a war between the country in scope and Brazil, no truces no treaties just an end to the fighting.


Check out this links religiously, look at the game code and other mods and just think about what could combine with what, good luck friend.
http://www.victoria2wiki.com/Full_list_of_effects
http://www.victoria2wiki.com/List_of_conditions
http://www.victoria2wiki.com/Full_list_of_scopes
http://www.victoria2wiki.com/Modifier_effects