Easy! Attack someone and look at your plunder number. Buy and ally and attack again. If your plunder number remains the same, you are at max plunder. If your plunder number changes, you need more allies.
READ Guide to ally ownership by TMH in "Best Of" Can't bump it because I'm on an iPhone or something.
Ok look at your stats you should have ••attack ••defense ••spy attack ••spy defense Assuming you don't have towers take The highest stat between attack or defense and add it to spy defense Eg 10,000attack. <- take this 9,700defense 1,000spy attack<- add to this 1,000spy defense That will give you 11,000 in total now for every 10,000 stats you have (out of the total you just worked out) buy 100mil worth of allies, so you would need 110mil for the above sum This is just a basic sum and it does vary between building types but it will get you on the right track
As for the attacking a player and testing method this is only good if you have a controlled farm as defense potions effect what you earn along with how many troops are alive in your kingdom