I recommend finding someone with attributes like genius, quick or stats like high intrigue, these will make your heirs have generally positive traits that are transferable over many generations and having good intrigue means that she can possibly become your spymaster and you can easily assassinate your sons if there are too many for your territories. Your guy isn't married so let's get that started. You have a bit of cash but if you want more the first thing you need to do is start conquering or raiding. When beginning as the Ylving you can see that you have 4 provinces and you can field around 1000 levies.