Don't take the missions too seriously, cancel them if they're too bad, otherwise just mind your own business until the opportunity comes along.
It's not just the missions, I realized a lot of my original goals were just going to make research impossible for centuries and increase colonization costs through the roof. So basically, maybe these goals could be achieved... On very easy. So basically, only way for a playable game was forming Russia. I sort of gave up on that game, in 1480, my Muscovy friend had grown over the Golden Horde and decided I was next target.
Novgorod is a merchant republic, so much for royal marriage hehe.