The problem with cardio is you could ask 1,000 different people and get 1,000 different answers. Here's what I like to do:
* I like to do low intensity fasted cardio. Most mornings I will go for a 45 minute-1 hour walk. Sometimes I will jog half the time. When fasted though my intensity is always LOW. If I really wanted to drop bodyfat I would go for fasted morning walks and a walk after my last meal.
* I like to do high intensity cardio at least twice a week. I run sprints at least twice a week. Not a LOT, but high in intensity. Your interval or HIIT type training would fit in here.
* I like to do many types of cardio. I'll jump rope, do complexes, go for long farmers walks, etc. Mix it up.
As for ab training I usually go 2-3 times per week. In one workout I'll focus on stabilization. This is where I hit planks, side planks, one legged planks on the ball, stir the pot, etc. In another workout I'll focus on "traditional" ab movements. This is where I hit swiss ball weighted crunches, hanging leg raises, and anything else typical. If I have three workouts I'll usually do static core work such as weighted side holds or rollouts. To me I don't understand why people treat abs any different than anything else. Hit them hard 2-3 times a week and you'll have success.
Hope this helps.