Is it ok to cut some extra wires that im not using from the psu? since i have a sff case, id rather just have the extra wires off instead of tucking them in places.
Do not twist them together. Cap each individually with electrical tape, then wrap the bundle well to make sure it doesn't come off. Make /damn/ sure you aren't going to need any of these wires in the future (don't cut off a currently unused 4 or 8 pin ATX power connector, say, or currently unused PCIe power connectors).
You certainly can cut them off without a problem. But like previous post stated make sure to insulate each wire within a connector bundle individually. Some one said make sure you don't need them later, but even if you do end up needing them its ok. It would be a royal pain in the butt and look really ugly but you could re-connect the wires later if you save all the harness' you cut off. If you think there is even a remote chance you would want to do this make sure to leave an inch or two sticking out of the psu.