A: Oh, I get confused, all right. But yes, there are, indeed, lots of things to watch out for in a series. The following are some things I've learned:
1. Keep a list of characters and places mentioned. With each addition to the series I add any changes to characters e.g.. hair grayer, cut off dreads, house burned, etc.
2. For ongoing characters, I've found it useful to construct family trees. You never know when the odd uncle or cousin will come in handy.
3. Keep a time line --I put events in real time (Vietnam War, Great flood of 1916), in bold; events in fictional (Miss Birdie born, Sam dies) time in regular.
4. Remember with each new book you have to reintroduce everyone all over again -- without boring faithful readers. I keep a small check list - describe Elizabeth, her house and farm, her family, her dogs, her back-story.
5. Be careful about how many ongoing characters you have-- it can begin to feel like you're pulling a heavy load, working everyone into every book -- or at least accounting for their absence. (Lee Child avoids this by having Jack Reacher constantly on the move -- new places, new faces in every book. )
6. Make sure your protagonist continues to evolve, to learn new things and reveal more and more of him or herself in every book. (My editor is really big on this one.)