The tach cable shouldn't be too hard to get, but will run about $30 or so. Ebay would be fine for that, especially if the seller is selling a oem honda part.
Any grips do the job really, it more comes down to personal preference. Thick grips made of soft rubber might wear a bit faster but will provide better grip and vibration dampening. Get grips with holes on the ends.
Then get yourself some bar-end mirrors. They are smaller than the stockers by quite a bit while still allowing you to see behind.
I haven't changed out signals or tail light, but dime city cycles has a lot of stuff like that. As long as the # of wires mtaches what you have now, it should work. LED bulbs require either an electronic flasher capable of handling them, or loads so they flash right.
The ride IS the adventure. The destination is just to get gas!