Just had a very strange but effective way of getting a full court happen to me. I started as Daimyo Hongo of Hyuga (vassal of Shimazu), and my leader died very early on having two sons, both from different mothers, and a regent ruler til they came of age. Out of sheer laugh factor, I betrothed each son to the mother of their half-brother, then forgot about it and went on to help my clan leader conquer our neighbor. Because of the interrelations between two brothers, and the different mothers not counting as being Inbred in the game mechanics, every child my brother had counted as a new brother/sister, increasing my court. I also got a bit lucky on three very fertile wives, and ended up with something like 8-9 children of my own before age 30. By 1500, my 4 kokujin, 2 vassal domain had an active court of 39 members, more than half of which were of age with a handful of landless in-laws to boot.
Something else to point out that I did not see mentioned above - for your first three wives, aim at any noble daughters you can either gain direct political advantage from (Uesugi, Yamana, Ouchi, etc), or any with a +Fertility bonus. Ignore their actual stats til the patch goes live, as only your most recent wife applies her stats to yours. Your 4th wife should have the best stats among the harem, I typically focus on Diplomacy with that one, though your own preference may vary depending on what stats you are lacking in.