Conditioning is two sided. You have oxygen supply and muscular demand. Without getting into the science of it, i would say work on the supply of oxygen by doing 1-2 hours of constant heart rate activity within the 130-150 bpm range. Hr rate monitors are reasonably priced and the most effective tool for conditioning. Omron has a model for 30 bucks.
For the muscular demand side of the equation, which i believe is what you are going for, you are trying to improve how efficient the muscles utilize oxygen. This helps in many sports that require significant muscular output for long periods, mma, wrestling, rugby, basketball, etc. Two of the best ways I have found to work this has been getting on a spin bike and turning the resistance up so that you are working at 25-30 rpm’s within a 155-165 hr rate range. If you dont have a spin bike, lunges are a great alternative within the same heart rate range. I use 20-25 lb dumbells in each hand for this. A weight vest is ideal. Step ups on a box about near waist height is a great way to do this training as well. Work both of those type of trainings and you will be able to perform optimally from a “cardio” perspective. I do sets of 20-30 minutes for this type of training, with 1-3 sets.
Depending on your sport different methods would be added into this to accomodate different aspects of the endurance spectrum. Most people, even atheletes have way to high a resting heart rate, which makes optimal performce in further rounds, plays, quarters etc difficult. Imagine you have to run a mile. You do the first lap in sub 60, but then further laps either your lungs or your legs hinder you from repeating that. You address the weak link (lungs or legs) then focus on improving that aspect of endurance.
Doing that many squats would be a hell of a load on your CNS. For your own sake i would say focus on a simple and effective powerlifting regimine and do the endurance methods I described on the off days or following lifting. The bike is great because it takes alot of the eccentric part out of the movement, which is usually responsible for your muscle soreness. When you are finished lifting, doing the muscular endurance training on a bike helps alot with your recovery as well.
8weeksout.com has much more detailed info than i have provided. Joel Jamison is agenius
fwiw, i used the above methods in tandem with starr’s 5x5 (intermediate and advanced) and put a ton of weight on my lifts but also improved conditioning simultaneously. They are not mutally exclusive.