This may be a stupid question, but what is the best way to find spouses?
I'm currently using the spouse finder, sorting by rank, and then browsing through to find the best options, but I've heard this isn't the best way. What other methods are better when planning for expansion?
I almost never worry about the prestige penalty, unless its my very first character in the dynasty and his ability to overcome negative prestige is dire. I also generally avoid the spouse finder unless I really want to just marry off the character and be done with it.
In the character finder you can always type in traits - "genius," "strong," "attractive." You can start getting to the point where you have people who are multi-generational geniuses and breed them with regularity into your main line. You can also use the character finder to find people to invite to your court, and therefor force a matrilineal marriage.
Planning for expansion? What title are you targetting? There's two ways to go, either check the immediate heirs, and see if any of them or their spouses might be invite-able. You can kill off the spouse and marry the heir, and get rid of any children who might be in the way.
The other way is to look at the list of claimants , and invite any which may be marriage material to your court. If they've got a title claim that will be inherited, and the title is below your current level, let it be inherited by the child who is one of your kin, then press the claim so that they become a vassal automatically. Once they're in your court they can't say no to a matrilineal marriage, either.
Otherwise, I generally avoid the spouse finder - way too few options.