My short wish list:
1) 51R battery with the correct battery tray. Does anyone know where I can buy this tray? I will cut my existing one if I need to but would prefer the right/correct tray for the larger battery. I found the 51R at Costco for $78. I want to do this.

2) A better horn. I read about the options. I want a louder horn that is plug and play. I don't want to solder or splice wires or add relays.

That's my short list. Long list coming soon. Maybe after dinner.

 

I believe evilchargerfan linked to a horn one that utilizes the OEM-Honda plug (single-pin). IIRC it is not inexpensive, but it could be exactly what you are looking for.