[rastilin]

also something I noticed is it a coincidence that all the masters have servents of the opposite gender, or is that some kind of rule?

Coincidence.

Spoiler for Fate:

During the 4th and 5th grail wars, servants get summoned or bound to masters of the same gender more often than not.

Lord El Melloi gets a Male Lancer
Tokiomi Tohsaka gets a Male Archer
Kotomine gets a Male Assassin (sort of)
Kariya Matou gets a Male Berzerker
Weaver Velvet gets a Male Rider
Ryuunosuke gets a Male Caster