There should be an option to appoint an heir at any time, but a player shouldn't be forced to. And, if the heir dies before becoming monarch, just appoint another. The benefit of appointing early would be to avoid any succession hassles, but might risk lowering the loyalty of some of the larger noble families (what, we can't be king now?) As well, appointing early, especially if an appoint as heir is FOR LIFE, might mean that an abler candidate won't be able to take the job later. Of course, if you wait too long and die, well, you might end up in a nasty civil war
As for sons and daughters, there's nothing PC aboit a woman ruling. Eleanor of Acquitaine springs to mind as just one example of a long list of women who were powerful in their own right. Of course, the attitudes of the times meant that mean were vastly preferred, and that should be reflected. Don't know if the varying customs can all be put in - that's a lot of coding - but it would sure be nice to see
