Hi hadesbox. 
Nintendo bending is relatively safe and you have lots of options. The best way you can learn really is to just get in there and play around. I always find that kind of answer annoying but it's true. A few things I can tell you though.... Potentiometers are great. Use low values (100ohms, single or 10turn) and patch them between glitch points. Input buffers are definitely the safest way to go for patching in external voltage signals. Don't be intimidated by this. Just use some op amps (TL074 is good). Look around with a multimeter to find a power source on the Nintendo circuit board. power your op amps off THat source. Then configure your op amps as voltage followers. By powering the opamp from the Nintendo it will ensure that the voltage coming out of the follower will never exceed the supply/nintendo voltage.it will also protect your synth from reverse current which is unlikely to be a problem anyway.