i dont think they could be any better than other civs. but i cant say because i never play as byzzies and i hate them.
if you want an espionage focused civ, try russia or prussia. or france, spain.
to build the st basils cathedral you just need a city with orthodoxy. the cathedral is cheap to build so you can make it in a crappy city.
to get orthodoxy, open up your borders with an orthodox civ (byzzies) so that they spread orthodoxy. or capture an orthodox city (in 600 AD map naples is best)
