For small small cuts im told to use peroxide, but is that good for large gashes as well?

No.... and no.: Do not use peroxide in cuts! while peroxide does kill the bacteria in the injury, it also kills all of your skin cells that are in the process of healing. It will delay healing and leave more of a scar. For most minor cuts, antimicrobial soap and water should be your choice. For larger cuts, see you doctor or er. They may need to suture the area. And remember you may need a tetanus vaccine!

Probably yes: Best advice if you are dealing with rapid loss of blood is to hold pressure untill bleeeding stops and seek medical care asap.