-start as Croatia (it's central country and catholic), quickly invade sicily
-then invade all the african coast
-make free investiture, but avoid to make antipopes if possible
-100% moral authority of catholic church is better
-DONT turn heretic (if you do so, no holy orders will be available + slow counties conversion due to 50% m.a.)
-DONT become an emperor (if you do so, you ll not be able to create kingdoms)
-give your coastal provinces to mayors - let them become doges in repubblics under your control (= LOTS of extra-money)
-elective agnatic succession
-make your child (male) become a heir to one empire, let him be tutored by a MUSLIM. perfet combination: your nationality BUT muslim. BUT dont make him inheredit your kingdom
-once he is legal age, claim the empire for him, so he is a MUSLIM emperor - that means you ALWAYS have a cb against the empire.
-repeat this step for all the 'big' kingdoms/empires
-consequences: BIG prestige for your House (because kings, emperors..), ALWAYS an infidel CB, quick counties conversion, YES holy orders etc etc...
p.s.: forgive my bad english..
Holy Muslim Roman Empire