Ultimately, you are going to want to use custom AI for Offense and Defense, or you will always have vulnerabilities. Personally I would never use a single of the preset plays on defense. Our AIs were built from the ground up, but I believe to save time you could copy and customize one of the preset AIs, changing the outputs to the plays you want to use specifically. Of course you could and will probably want to soon start adding new Inputs to your AI to cover situations the basic pre-made AIs usually do not, as well. One of them should give you a good starting point though!
Offensively, you'll want to use your "custom O slots" in the depth chart, and make sure the outputs in the AI utilize the correct "Depth Chart" for the players you want in on those play calls. Typically, people will use the #1 slot for power and #2 slot for speed- for example, the power HB can be HB1 and the speed or scatback as HB2, the blocking TE at TE1 and the receiving TE at TE2, etc. Then for example, if its an outside run, use RB2 in the output with the play, if the TE is lead blocking use TE1, etc. The only thing is you don't necessarily want is to be too obvious so maybe use a few plays with the power back running outside, the blocking TE in on a pass play, etc, you know, so the other team just can't jump all over whatever you're trying to do. How you balance that is often a major key to how good your offense can be. All that might be getting a little advanced for just starting off though. First thing is to get the right players at the custom O slots you want them at, then make sure the plays in the outputs of the AI you use are utilizing the custom O slots how you intend.