Do I really need to use these sensors. If I do not use the sensors, could anything bad happen. I am ordering wheels and tires online and they will be already mounted . I know I should be using them but can I get buy without them for now.

Any good tire store will offer you the correct sensors with your wheels, sure you do not have to use them, you will just get a warning every time you start your truck. Of course not using them with big wheels and tires could cause you a problem, if you have a tire issue and lose air quickly you could ruin your wheels because you will get no warning without the sensors.

You should use them. They're easy to find ;)