@Kraviz i recommend starting a time run at 25 minutes and keeping your heartrate at 60 - 75% of your maximum. this is about 132 - 165 heart beats a minute. if you are truly hitting the weights like you are saying then you should go for a low to mid range. so 132 - 150. you need to make sure though that you are hitting your anaerobic threshold during weight lifting to have full workout. each week increase the speed but stay in that range. after awhile you will be able to run faster and still keep that heartrate range easily.
also you don't have to just do running you can do swimming and jump rope. running is just a very easy way to measure progress because of timing and speed increase. you can do the same with jump roping and swimming. you can count the numbers of jumps per minute and you can count the number laps per workout session in the pool. just stay within that range.
hitting the heavy bag can be done too. you can count how many times you hit the bag with your power hand and your jab. if you do martial arts practicing shadow boxing in a routine form can be counted how many times you completed it before time was up.
best warmup is the same movements with lower weight, and before that dynamic stretching which puts the joints you will be moving through their full range of movement, without holding positions for longer than a few seconds
