If you have started going to the farm automatically, your stats (intelligence and willpower) should lower whenever you do. If you go under a certain level (intelligence should go below 60), you unlock the final stage of the cowgirl path. If you are having problems, you can use the travel sphere (the debug tool in the key items): there is a red sphere in the top-left corner of the room, and it allows you to change your stats at will.
If you make your choice about the book and then finish the main quest, you get to see the consequences durign the ending. These won't happen right away, but some years in the future. As for the endings:
Unless something changed since I last played once you're on Vamp route Whatshername will telepathically stop you from going anywhere near the Zantis because the Vampires know very well what that lot is up to. Ie. they're mutually exclusive. (Also means if you want to complete the Zanti investigation quest you need to do so before getting too involved with the alarmingly pale chick you only see out and about at night.)
Both paths are featured in the ending (but, as someone already pointed out, they are mutually exclusive). Both of these paths unlock some unique quests, and affect existing ones by forcing you to take a certain side/route to solve them (usually to the benefit of the faction), assuming you haven't solved the quests already, obviously.
If I remember correctly, I made it so you can still get caught (and brainwashed into saying that everything is fine at the farm) but the mental block from Beatrix is still present, so you'll still avoid the farm afterward.
You must go to Golden Leaf, a town in the east-south-east of Caliross (it's the area of the map where it starts raining). The mansion is to the north of the square (past a small wooden bridge). You can buy a carriage as a noble, but only after Keiko tells you about it, so you must first go there by foot.
If you have unlocked the transformation at the end of the third temple, and you need to enter the magic academy, she is a possible "target" for that transformation, otherwise there isn't much to do there.
