great looking bike, I wish I had the space for those kinds of projects. a hobby shop (you know a good one that sells build it yourself RC stuff) may have something you can use for a horn.
as for grease.. unless the rear hub have an oil port there is no way to grease the bearings without taking it apart. the hubs, headset and bottom bracket should al be taken apart and greased. the best grease is the expensive bicycle grease like Park, Pedros and Phil Wood, but any highspped waterproof bearing grease is good.
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk