About half an hour after writing this, I discovered the best way of maximising the spirit system. If when training a slave, you aim for the dating perk (The flower) you're able to use dates to increase loyalty by 20+ a time, also after a few successful dates and intimate talks, you'll unlock them naturally wanting sex, so you only need to train 3-5 times, and then date farm until you've unlocked all of the perks. Make sure to aim for what specialisation you're wanting with the slave in question, worker, sexual or fighter, when using the train feature. Then date until all is unlocked to complete the training.
Best of luck, Masters. :)