Your nutes that you have should tell you when and how often to feed. Your plants and medium will be different than the next person, so if your not sure follow your nutes recommended feeding schedule and adjust from there. As for the cutting off some of the bottom I'd recommend it. It is called lollipop method and it is used a lot. The bottom branches create little fluffy buds that are not very desirable, so if you remove the lower part of the plant it allows for more energy to go to growing the top buds. If you check out some journals you will notice a lot of bare plants at the bottom, this isn't naturally.