1. whatever you do, DONT land your heir. he will turn into an demons spawn and get so bad even the demons spawn is horrified by his sins. i often see him picking up kinslayer if i have a lot of relatives as well.
2. there seems to be a thought that civil wars are bad. in thruth, only LARGE civil wars are bad, small ones are an blessing. they allow you to pick up prestig, revoke some titles from the largest troublemakers, break their powerbase, and then distribute these titles to new lords that are now loyal to you. on top of this, you also get to imprison them so they will never bother you again if you dont let em out.
3. landing family for non RP purposes is an double-edged sword. on one hand, they help eachother and regulary expand on their own, increasing your own power and having you not bother with expansion, with the hidden benefit that this lowers their millitary power and thus making their factions weaker, and have an free +5 modifier with you. on the other side, they intermarry like crazy and can form superdukes like that, a small succession war in the duchy of nowheristan can set the realm ablaze and prevent succession law changes and their claims on your titles can often be very annoying, although in elective any duke can start an faction anyways. the dysnatic prestige beats all though, as getting a free 100+ prestige on your heirs birth and possibly with marriage is just plain awesome.