The civil wars are constant; no matter who you are playing. 

A couple of suggestations to avoid civil wars. 

1.  Promote Bishops to Count (Metropolitan).  As soon as they die, their title returns to you.  The problem of making a Baron a Count is relations are hereditary (so if a Count hates you, so will his son).

Also avoid creating a Kingdom if you are not an elective monarchy, because the end result is you'll have powerful Dukes (even if they are Bishops) who'll eventually make up an excuse to rebel against your heir.

2.  Elective Monarchy,

Remember – it's not the character you are playing but the Dynasty, so essentially anyone you nominate in an elective monarchy (even if they don't win) will become your heir (as long as they are of your Dynasty.  Even if they are distantly related).  Make sure to hand out elective titles to people within your dynasty, to avoid the scenario of potentially losing the game (you need a heir is a Count in rank)

3.  Remove taxes on vassals and church.  Although, you can probably keep city taxes on max because (unless you are retarded!) you probably won't promote a Mayor to run a county.  Anyway, taxes simply don't contribute much to your income.  Most of your income comes from your personal Demense and especially if you are holding cities with upgrades, you'll easily be making at least 10-20 gold a month.

4.  Imprison people.  Intrigue / Plots, arrest people who are a leader of a Plot.  Each person you release out of jail will gain you +10 opinion with your vassals.  So if you have arrested 20 leaders of plots (without penalty), if your heir inherits (which pisses people off), then simply empty the jails to avoid the sucession civil wars.

A hint for Rus

Play as the Duke of Galich, assassinate your first son and your titles will pass to your second son, who is the Duke of Novgorod and the result (when your character dies) is about 42% of the requirement to create the Kingdom of Rus.