Ok, let us assume that I want to give a Digimon +30 on everything and 10 in sp, what would I have to do?
First your Digimon (named Art) must have 100 ABI. Then you look at his personality, lets say Art has a Brainy personality which when training in the farm will increase their INT. Put him in the farm with another Digimon (named Bit), lets say Bit has a Fighter personality which increases ATK when training.
Understand the concept that when training, a Digimon will increase its stats based on it's own personality and its leader personality. Based on that, we can have Art be the leader and since he's the leader then he will gain stat only on INT. Meanwhile, Bit will gain stat for both ATK and INT because his leader is Brainy while he has a Fighter personality. The same will happen if Bit become leader; Art will gain both ATK and INT while Bit will only gain ATK.
Let's tackle your scenario now; for example we want +30 in ATK, DEF and INT with +10 in SP. We have Art and Bit in the farm and we made Bit the leader. After a while, Art will have gained 30 bonus stats on both ATK and INT. Now we need to increase his DEF and SP; we give him a Defender Patch to change his personality to Defender which will make him gain DEF. We make another Digimon (named Cor) who has a Lively personality which will increase SP as the leader so that Art gain both DEF and SP. Once he gained 10 SP, we change the leader back to Art so that he only gains DEF. We leave him till he maxed out his DEF at 30 and Art's training is finally finish.
Now Art has +30 in ATK, DEF and INT with +10 in SP, maxing out his potential with 100 gained bonus stats.